diff --git a/src/chat.cpp b/src/chat.cpp
index 1fb872b85..2d29d39da 100644
--- a/src/chat.cpp
+++ b/src/chat.cpp
@@ -83,7 +83,7 @@ u32 ChatBuffer::getScrollback() const
 
 const ChatLine& ChatBuffer::getLine(u32 index) const
 {
-	assert(index < getLineCount());
+	assert(index < getLineCount());	// pre-condition
 	return m_unformatted[index];
 }
 
@@ -107,7 +107,8 @@ void ChatBuffer::deleteOldest(u32 count)
 		// keep m_formatted in sync
 		if (del_formatted < m_formatted.size())
 		{
-			assert(m_formatted[del_formatted].first);
+
+			sanity_check(m_formatted[del_formatted].first);
 			++del_formatted;
 			while (del_formatted < m_formatted.size() &&
 					!m_formatted[del_formatted].first)
diff --git a/src/client.cpp b/src/client.cpp
index 00b79e92e..edf244452 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -97,7 +97,7 @@ void MeshUpdateQueue::addBlock(v3s16 p, MeshMakeData *data, bool ack_block_to_se
 {
 	DSTACK(__FUNCTION_NAME);
 
-	assert(data);
+	assert(data);	// pre-condition
 
 	JMutexAutoLock lock(m_mutex);
 
@@ -388,8 +388,9 @@ void Client::step(float dtime)
 		if(counter <= 0.0) {
 			counter = 2.0;
 
-			Player *myplayer = m_env.getLocalPlayer();
-			assert(myplayer != NULL);
+			Player *myplayer = m_env.getLocalPlayer();		
+			FATAL_ERROR_IF(myplayer == NULL, "Local player not found in environment.");
+
 			// Send TOSERVER_INIT
 			// [0] u16 TOSERVER_INIT
 			// [2] u8 SER_FMT_VER_HIGHEST_READ
@@ -707,7 +708,9 @@ bool Client::loadMedia(const std::string &data, const std::string &filename)
 		// Create an irrlicht memory file
 		io::IReadFile *rfile = irrfs->createMemoryReadFile(
 				*data_rw, data_rw.getSize(), "_tempreadfile");
-		assert(rfile);
+
+		FATAL_ERROR_IF(!rfile, "Could not create irrlicht memory file.");
+
 		// Read image
 		video::IImage *img = vdrv->createImageFromFile(rfile);
 		if(!img){
@@ -785,7 +788,8 @@ void Client::request_media(const std::vector<std::string> &file_requests)
 	std::ostringstream os(std::ios_base::binary);
 	writeU16(os, TOSERVER_REQUEST_MEDIA);
 	size_t file_requests_size = file_requests.size();
-	assert(file_requests_size <= 0xFFFF);
+
+	FATAL_ERROR_IF(file_requests_size > 0xFFFF, "Unsupported number of file requests");
 
 	// Packet dynamicly resized
 	NetworkPacket* pkt = new NetworkPacket(TOSERVER_REQUEST_MEDIA, 2 + 0);
@@ -986,7 +990,8 @@ void Client::sendNodemetaFields(v3s16 p, const std::string &formname,
 		const std::map<std::string, std::string> &fields)
 {
 	size_t fields_size = fields.size();
-	assert(fields_size <= 0xFFFF);
+
+	FATAL_ERROR_IF(fields_size > 0xFFFF, "Unsupported number of nodemeta fields");
 
 	NetworkPacket* pkt = new NetworkPacket(TOSERVER_NODEMETA_FIELDS, 0);
 
@@ -1007,7 +1012,7 @@ void Client::sendInventoryFields(const std::string &formname,
 		const std::map<std::string, std::string> &fields)
 {
 	size_t fields_size = fields.size();
-	assert(fields_size <= 0xFFFF);
+	FATAL_ERROR_IF(fields_size > 0xFFFF, "Unsupported number of inventory fields");
 
 	NetworkPacket* pkt = new NetworkPacket(TOSERVER_INVENTORY_FIELDS, 0);
 	*pkt << formname << (u16) (fields_size & 0xFFFF);
@@ -1141,7 +1146,7 @@ void Client::sendPlayerPos()
 	// Set peer id if not set already
 	if(myplayer->peer_id == PEER_ID_INEXISTENT)
 		myplayer->peer_id = our_peer_id;
-	// Check that an existing peer_id is the same as the connection's
+
 	assert(myplayer->peer_id == our_peer_id);
 
 	v3f pf         = myplayer->getPosition();
@@ -1179,8 +1184,6 @@ void Client::sendPlayerItem(u16 item)
 	// Set peer id if not set already
 	if(myplayer->peer_id == PEER_ID_INEXISTENT)
 		myplayer->peer_id = our_peer_id;
-
-	// Check that an existing peer_id is the same as the connection's
 	assert(myplayer->peer_id == our_peer_id);
 
 	NetworkPacket* pkt = new NetworkPacket(TOSERVER_PLAYERITEM, 2);
@@ -1295,7 +1298,7 @@ Inventory* Client::getInventory(const InventoryLocation &loc)
 	}
 	break;
 	default:
-		assert(0);
+		FATAL_ERROR("Invalid inventory location type.");
 	}
 	return NULL;
 }
@@ -1555,9 +1558,9 @@ float Client::mediaReceiveProgress()
 void Client::afterContentReceived(IrrlichtDevice *device, gui::IGUIFont* font)
 {
 	infostream<<"Client::afterContentReceived() started"<<std::endl;
-	assert(m_itemdef_received);
-	assert(m_nodedef_received);
-	assert(mediaReceived());
+	assert(m_itemdef_received); // pre-condition
+	assert(m_nodedef_received); // pre-condition
+	assert(mediaReceived()); // pre-condition
 
 	const wchar_t* text = wgettext("Loading textures...");
 
@@ -1697,9 +1700,10 @@ scene::ISceneManager* Client::getSceneManager()
 }
 u16 Client::allocateUnknownNodeId(const std::string &name)
 {
-	errorstream<<"Client::allocateUnknownNodeId(): "
-			<<"Client cannot allocate node IDs"<<std::endl;
-	assert(0);
+	errorstream << "Client::allocateUnknownNodeId(): "
+			<< "Client cannot allocate node IDs" << std::endl;
+	FATAL_ERROR("Client allocated unknown node");
+
 	return CONTENT_IGNORE;
 }
 ISoundManager* Client::getSoundManager()
@@ -1734,7 +1738,7 @@ scene::IAnimatedMesh* Client::getMesh(const std::string &filename)
 	io::IFileSystem *irrfs = m_device->getFileSystem();
 	io::IReadFile *rfile   = irrfs->createMemoryReadFile(
 			*data_rw, data_rw.getSize(), filename.c_str());
-	assert(rfile);
+	FATAL_ERROR_IF(!rfile, "Could not create/open RAM file");
 
 	scene::IAnimatedMesh *mesh = smgr->getMesh(rfile);
 	rfile->drop();
diff --git a/src/client/clientlauncher.cpp b/src/client/clientlauncher.cpp
index 0f60dcd63..7bf849624 100644
--- a/src/client/clientlauncher.cpp
+++ b/src/client/clientlauncher.cpp
@@ -128,7 +128,7 @@ bool ClientLauncher::run(GameParams &game_params, const Settings &cmd_args)
 	skin->setColor(gui::EGDC_HIGH_LIGHT_TEXT, video::SColor(255, 255, 255, 255));
 
 	g_fontengine = new FontEngine(g_settings, guienv);
-	assert(g_fontengine != NULL);
+	FATAL_ERROR_IF(g_fontengine == NULL, "Font engine creation failed.");
 
 #if (IRRLICHT_VERSION_MAJOR >= 1 && IRRLICHT_VERSION_MINOR >= 8) || IRRLICHT_VERSION_MAJOR >= 2
 	// Irrlicht 1.8 input colours
diff --git a/src/client/tile.cpp b/src/client/tile.cpp
index e5d02de7c..541247fa8 100644
--- a/src/client/tile.cpp
+++ b/src/client/tile.cpp
@@ -199,7 +199,7 @@ public:
 	void insert(const std::string &name, video::IImage *img,
 			bool prefer_local, video::IVideoDriver *driver)
 	{
-		assert(img);
+		assert(img); // Pre-condition
 		// Remove old image
 		std::map<std::string, video::IImage*>::iterator n;
 		n = m_images.find(name);
@@ -423,7 +423,7 @@ IWritableTextureSource* createTextureSource(IrrlichtDevice *device)
 TextureSource::TextureSource(IrrlichtDevice *device):
 		m_device(device)
 {
-	assert(m_device);
+	assert(m_device); // Pre-condition
 
 	m_main_thread = get_current_thread_id();
 
@@ -597,7 +597,7 @@ u32 TextureSource::generateTexture(const std::string &name)
 	}
 
 	video::IVideoDriver *driver = m_device->getVideoDriver();
-	assert(driver);
+	sanity_check(driver);
 
 	video::IImage *img = generateImage(name);
 
@@ -684,7 +684,7 @@ void TextureSource::insertSourceImage(const std::string &name, video::IImage *im
 {
 	//infostream<<"TextureSource::insertSourceImage(): name="<<name<<std::endl;
 
-	assert(get_current_thread_id() == m_main_thread);
+	sanity_check(get_current_thread_id() == m_main_thread);
 
 	m_sourcecache.insert(name, img, true, m_device->getVideoDriver());
 	m_source_image_existence.set(name, true);
@@ -695,7 +695,7 @@ void TextureSource::rebuildImagesAndTextures()
 	JMutexAutoLock lock(m_textureinfo_cache_mutex);
 
 	video::IVideoDriver* driver = m_device->getVideoDriver();
-	assert(driver != 0);
+	sanity_check(driver);
 
 	// Recreate textures
 	for (u32 i=0; i<m_textureinfo_cache.size(); i++){
@@ -703,8 +703,8 @@ void TextureSource::rebuildImagesAndTextures()
 		video::IImage *img = generateImage(ti->name);
 #ifdef __ANDROID__
 		img = Align2Npot2(img, driver);
-		assert(img->getDimension().Height == npot2(img->getDimension().Height));
-		assert(img->getDimension().Width == npot2(img->getDimension().Width));
+		sanity_check(img->getDimension().Height == npot2(img->getDimension().Height));
+		sanity_check(img->getDimension().Width == npot2(img->getDimension().Width));
 #endif
 		// Create texture from resulting image
 		video::ITexture *t = NULL;
@@ -725,7 +725,7 @@ video::ITexture* TextureSource::generateTextureFromMesh(
 		const TextureFromMeshParams &params)
 {
 	video::IVideoDriver *driver = m_device->getVideoDriver();
-	assert(driver);
+	sanity_check(driver);
 
 #ifdef __ANDROID__
 	const GLubyte* renderstr = glGetString(GL_RENDERER);
@@ -741,9 +741,9 @@ video::ITexture* TextureSource::generateTextureFromMesh(
 		) {
 		// Get a scene manager
 		scene::ISceneManager *smgr_main = m_device->getSceneManager();
-		assert(smgr_main);
+		sanity_check(smgr_main);
 		scene::ISceneManager *smgr = smgr_main->createNewSceneManager();
-		assert(smgr);
+		sanity_check(smgr);
 
 		const float scaling = 0.2;
 
@@ -978,7 +978,7 @@ video::IImage* TextureSource::generateImage(const std::string &name)
 
 
 	video::IVideoDriver* driver = m_device->getVideoDriver();
-	assert(driver);
+	sanity_check(driver);
 
 	/*
 		Parse out the last part of the name of the image and act
@@ -1078,7 +1078,7 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 		video::IImage *& baseimg)
 {
 	video::IVideoDriver* driver = m_device->getVideoDriver();
-	assert(driver);
+	sanity_check(driver);
 
 	// Stuff starting with [ are special commands
 	if (part_of_name.size() == 0 || part_of_name[0] != '[')
@@ -1106,7 +1106,7 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 			//core::dimension2d<u32> dim(2,2);
 			core::dimension2d<u32> dim(1,1);
 			image = driver->createImage(video::ECF_A8R8G8B8, dim);
-			assert(image);
+			sanity_check(image != NULL);
 			/*image->setPixel(0,0, video::SColor(255,255,0,0));
 			image->setPixel(1,0, video::SColor(255,0,255,0));
 			image->setPixel(0,1, video::SColor(255,0,0,255));
@@ -1362,7 +1362,7 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 					transform, baseimg->getDimension());
 			video::IImage *image = driver->createImage(
 					baseimg->getColorFormat(), dim);
-			assert(image);
+			sanity_check(image != NULL);
 			imageTransform(transform, baseimg, image);
 			baseimg->drop();
 			baseimg = image;
@@ -1422,7 +1422,7 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 					(imagename_left + "__temp__").c_str(), img_left);
 			video::ITexture *texture_right = driver->addTexture(
 					(imagename_right + "__temp__").c_str(), img_right);
-			assert(texture_top && texture_left && texture_right);
+			FATAL_ERROR_IF(!(texture_top && texture_left && texture_right), "");
 
 			// Drop images
 			img_top->drop();
@@ -1476,7 +1476,7 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 
 			// Create image of render target
 			video::IImage *image = driver->createImage(rtt, v2s32(0, 0), params.dim);
-			assert(image);
+			FATAL_ERROR_IF(!image, "Could not create image of render target");
 
 			// Cleanup texture
 			driver->removeTexture(rtt);
@@ -1892,10 +1892,10 @@ void imageTransform(u32 transform, video::IImage *src, video::IImage *dst)
 	if (src == NULL || dst == NULL)
 		return;
 
-	core::dimension2d<u32> srcdim = src->getDimension();
 	core::dimension2d<u32> dstdim = dst->getDimension();
 
-	assert(dstdim == imageTransformDimension(transform, srcdim));
+	// Pre-conditions
+	assert(dstdim == imageTransformDimension(transform, src->getDimension()));
 	assert(transform <= 7);
 
 	/*
diff --git a/src/clientiface.h b/src/clientiface.h
index 2f265b128..cc303734a 100644
--- a/src/clientiface.h
+++ b/src/clientiface.h
@@ -426,9 +426,12 @@ public:
 	/* event to update client state */
 	void event(u16 peer_id, ClientStateEvent event);
 
-	/* set environment */
-	void setEnv(ServerEnvironment* env)
-	{ assert(m_env == 0); m_env = env; }
+	/* Set environment. Do not call this function if environment is already set */
+	void setEnv(ServerEnvironment *env)
+	{
+		assert(m_env == NULL); // pre-condition
+		m_env = env;
+	}
 
 	static std::string state2Name(ClientState state);
 
diff --git a/src/clientmap.cpp b/src/clientmap.cpp
index 1c420b5f9..907df7128 100644
--- a/src/clientmap.cpp
+++ b/src/clientmap.cpp
@@ -102,34 +102,6 @@ MapSector * ClientMap::emergeSector(v2s16 p2d)
 	return sector;
 }
 
-#if 0
-void ClientMap::deSerializeSector(v2s16 p2d, std::istream &is)
-{
-	DSTACK(__FUNCTION_NAME);
-	ClientMapSector *sector = NULL;
-
-	//JMutexAutoLock lock(m_sector_mutex); // Bulk comment-out
-
-	core::map<v2s16, MapSector*>::Node *n = m_sectors.find(p2d);
-
-	if(n != NULL)
-	{
-		sector = (ClientMapSector*)n->getValue();
-		assert(sector->getId() == MAPSECTOR_CLIENT);
-	}
-	else
-	{
-		sector = new ClientMapSector(this, p2d);
-		{
-			//JMutexAutoLock lock(m_sector_mutex); // Bulk comment-out
-			m_sectors.insert(p2d, sector);
-		}
-	}
-
-	sector->deSerialize(is);
-}
-#endif
-
 void ClientMap::OnRegisterSceneNode()
 {
 	if(IsVisible)
diff --git a/src/clientmedia.cpp b/src/clientmedia.cpp
index 1d825c143..0918e8a37 100644
--- a/src/clientmedia.cpp
+++ b/src/clientmedia.cpp
@@ -72,7 +72,7 @@ ClientMediaDownloader::~ClientMediaDownloader()
 
 void ClientMediaDownloader::addFile(std::string name, std::string sha1)
 {
-	assert(!m_initial_step_done);
+	assert(!m_initial_step_done); // pre-condition
 
 	// if name was already announced, ignore the new announcement
 	if (m_files.count(name) != 0) {
@@ -107,7 +107,7 @@ void ClientMediaDownloader::addFile(std::string name, std::string sha1)
 
 void ClientMediaDownloader::addRemoteServer(std::string baseurl)
 {
-	assert(!m_initial_step_done);
+	assert(!m_initial_step_done);	// pre-condition
 
 	#ifdef USE_CURL
 
@@ -356,11 +356,11 @@ void ClientMediaDownloader::remoteMediaReceived(
 		m_remote_file_transfers.erase(it);
 	}
 
-	assert(m_files.count(name) != 0);
+	sanity_check(m_files.count(name) != 0);
 
 	FileStatus *filestatus = m_files[name];
-	assert(!filestatus->received);
-	assert(filestatus->current_remote >= 0);
+	sanity_check(!filestatus->received);
+	sanity_check(filestatus->current_remote >= 0);
 
 	RemoteServerStatus *remote = m_remotes[filestatus->current_remote];
 
@@ -382,6 +382,7 @@ void ClientMediaDownloader::remoteMediaReceived(
 
 s32 ClientMediaDownloader::selectRemoteServer(FileStatus *filestatus)
 {
+	// Pre-conditions
 	assert(filestatus != NULL);
 	assert(!filestatus->received);
 	assert(filestatus->current_remote < 0);
@@ -483,7 +484,7 @@ void ClientMediaDownloader::startRemoteMediaTransfers()
 
 void ClientMediaDownloader::startConventionalTransfers(Client *client)
 {
-	assert(m_httpfetch_active == 0);
+	assert(m_httpfetch_active == 0);	// pre-condition
 
 	if (m_uncached_received_count != m_uncached_count) {
 		// Some media files have not been received yet, use the
@@ -616,7 +617,7 @@ std::string ClientMediaDownloader::serializeRequiredHashSet()
 			it = m_files.begin();
 			it != m_files.end(); ++it) {
 		if (!it->second->received) {
-			assert(it->second->sha1.size() == 20);
+			FATAL_ERROR_IF(it->second->sha1.size() != 20, "Invalid SHA1 size");
 			os << it->second->sha1;
 		}
 	}
diff --git a/src/collision.cpp b/src/collision.cpp
index b1b1e23bd..12eabff09 100644
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -173,7 +173,7 @@ bool wouldCollideWithCeiling(
 {
 	//TimeTaker tt("wouldCollideWithCeiling");
 
-	assert(y_increase >= 0);
+	assert(y_increase >= 0);	// pre-condition
 
 	for(std::vector<aabb3f>::const_iterator
 			i = staticboxes.begin();
@@ -348,11 +348,11 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		}
 	} //tt3
 
-	assert(cboxes.size() == is_unloaded.size());
-	assert(cboxes.size() == is_step_up.size());
-	assert(cboxes.size() == bouncy_values.size());
-	assert(cboxes.size() == node_positions.size());
-	assert(cboxes.size() == is_object.size());
+	assert(cboxes.size() == is_unloaded.size());    // post-condition
+	assert(cboxes.size() == is_step_up.size());     // post-condition
+	assert(cboxes.size() == bouncy_values.size());  // post-condition
+	assert(cboxes.size() == node_positions.size()); // post-condition
+	assert(cboxes.size() == is_object.size());      // post-condition
 
 	/*
 		Collision detection
@@ -367,7 +367,7 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 	//f32 d = 0.15*BS;
 
 	// This should always apply, otherwise there are glitches
-	assert(d > pos_max_d);
+	assert(d > pos_max_d);	// invariant
 
 	int loopcount = 0;
 
diff --git a/src/content_cao.cpp b/src/content_cao.cpp
index 5c3c7b54c..4c8962edb 100644
--- a/src/content_cao.cpp
+++ b/src/content_cao.cpp
@@ -1718,10 +1718,12 @@ void GenericCAO::processMessage(const std::string &data)
 	}
 }
 	
+/* \pre punchitem != NULL
+ */
 bool GenericCAO::directReportPunch(v3f dir, const ItemStack *punchitem,
 		float time_from_last_punch)
 {
-	assert(punchitem);
+	assert(punchitem);	// pre-condition
 	const ToolCapabilities *toolcap =
 			&punchitem->getToolCapabilities(m_gamedef->idef());
 	PunchDamageResult result = getPunchDamage(
diff --git a/src/content_mapblock.cpp b/src/content_mapblock.cpp
index 3428f85f9..2f1368765 100644
--- a/src/content_mapblock.cpp
+++ b/src/content_mapblock.cpp
@@ -47,7 +47,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 void makeCuboid(MeshCollector *collector, const aabb3f &box,
 	TileSpec *tiles, int tilecount, video::SColor &c, const f32* txc)
 {
-	assert(tilecount >= 1 && tilecount <= 6);
+	assert(tilecount >= 1 && tilecount <= 6); // pre-condition
 
 	v3f min = box.MinEdge;
 	v3f max = box.MaxEdge;
@@ -206,8 +206,8 @@ void mapblock_mesh_generate_special(MeshMakeData *data,
 
 		switch(f.drawtype){
 		default:
-			infostream<<"Got "<<f.drawtype<<std::endl;
-			assert(0);
+			infostream << "Got " << f.drawtype << std::endl;
+			FATAL_ERROR("Unknown drawtype");
 			break;
 		case NDT_AIRLIKE:
 			break;
@@ -754,7 +754,7 @@ void mapblock_mesh_generate_special(MeshMakeData *data,
 		break;}
 		case NDT_GLASSLIKE_FRAMED_OPTIONAL:
 			// This is always pre-converted to something else
-			assert(0);
+			FATAL_ERROR("NDT_GLASSLIKE_FRAMED_OPTIONAL not pre-converted as expected");
 			break;
 		case NDT_GLASSLIKE_FRAMED:
 		{
@@ -1006,7 +1006,7 @@ void mapblock_mesh_generate_special(MeshMakeData *data,
 		break;}
 		case NDT_ALLFACES_OPTIONAL:
 			// This is always pre-converted to something else
-			assert(0);
+			FATAL_ERROR("NDT_ALLFACES_OPTIONAL not pre-converted");
 			break;
 		case NDT_TORCHLIKE:
 		{
diff --git a/src/content_sao.cpp b/src/content_sao.cpp
index 9b2e41677..e58aa4b6e 100644
--- a/src/content_sao.cpp
+++ b/src/content_sao.cpp
@@ -724,8 +724,8 @@ PlayerSAO::PlayerSAO(ServerEnvironment *env_, Player *player_, u16 peer_id_,
 	m_physics_override_sneak_glitch(true),
 	m_physics_override_sent(false)
 {
-	assert(m_player);
-	assert(m_peer_id != 0);
+	assert(m_player);	// pre-condition
+	assert(m_peer_id != 0);	// pre-condition
 	setBasePosition(m_player->getPosition());
 	m_inventory = &m_player->inventory;
 	m_armor_groups["fleshy"] = 100;
@@ -833,7 +833,7 @@ std::string PlayerSAO::getClientInitializationData(u16 protocol_version)
 
 std::string PlayerSAO::getStaticData()
 {
-	assert(0);
+	FATAL_ERROR("Deprecated function (?)");
 	return "";
 }
 
diff --git a/src/database-sqlite3.cpp b/src/database-sqlite3.cpp
index 3480894c9..c937cae31 100644
--- a/src/database-sqlite3.cpp
+++ b/src/database-sqlite3.cpp
@@ -210,14 +210,13 @@ std::string Database_SQLite3::loadBlock(const v3s16 &pos)
 
 void Database_SQLite3::createDatabase()
 {
-	assert(m_database);
+	assert(m_database); // Pre-condition
 	SQLOK(sqlite3_exec(m_database,
 		"CREATE TABLE IF NOT EXISTS `blocks` (\n"
 		"	`pos` INT PRIMARY KEY,\n"
 		"	`data` BLOB\n"
 		");\n",
 		NULL, NULL, NULL));
-
 }
 
 void Database_SQLite3::listAllLoadableBlocks(std::vector<v3s16> &dst)
diff --git a/src/debug.cpp b/src/debug.cpp
index bd970a8e4..521891bbd 100644
--- a/src/debug.cpp
+++ b/src/debug.cpp
@@ -133,11 +133,11 @@ Nullstream dummyout;
 	Assert
 */
 
-void assert_fail(const char *assertion, const char *file,
+void sanity_check_fn(const char *assertion, const char *file,
 		unsigned int line, const char *function)
 {
 	DEBUGPRINT("\nIn thread %lx:\n"
-			"%s:%u: %s: Assertion '%s' failed.\n",
+			"%s:%u: %s: An engine assumption '%s' failed.\n",
 			(unsigned long)get_current_thread_id(),
 			file, line, function, assertion);
 
@@ -149,6 +149,22 @@ void assert_fail(const char *assertion, const char *file,
 	abort();
 }
 
+void fatal_error_fn(const char *msg, const char *file,
+		unsigned int line, const char *function)
+{
+	DEBUGPRINT("\nIn thread %lx:\n"
+			"%s:%u: %s: A fatal error occurred: %s\n",
+			(unsigned long)get_current_thread_id(),
+			file, line, function, msg);
+
+	debug_stacks_print();
+
+	if(g_debugstreams[1])
+		fclose(g_debugstreams[1]);
+
+	abort();
+}
+
 /*
 	DebugStack
 */
diff --git a/src/debug.h b/src/debug.h
index 1027fde69..9684aa2df 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -22,6 +22,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include <iostream>
 #include <exception>
+#include <assert.h>
 #include "gettime.h"
 
 #if (defined(WIN32) || defined(_WIN32_WCE))
@@ -72,28 +73,38 @@ extern std::ostream dstream;
 extern std::ostream dstream_no_stderr;
 extern Nullstream dummyout;
 
-/*
-	Include assert.h and immediately undef assert so that it can't override
-	our assert later on. leveldb/slice.h is a notable offender.
-*/
 
-#include <assert.h>
-#undef assert
+/* Abort program execution immediately
+ */
+__NORETURN extern void fatal_error_fn(
+		const char *msg, const char *file,
+		unsigned int line, const char *function);
+
+#define FATAL_ERROR(msg) \
+	fatal_error_fn((msg), __FILE__, __LINE__, __FUNCTION_NAME)
+
+#define FATAL_ERROR_IF(expr, msg) \
+	((expr) \
+	? fatal_error_fn((msg), __FILE__, __LINE__, __FUNCTION_NAME) \
+	: (void)(0))
 
 /*
-	Assert
+	sanity_check()
+	Equivalent to assert() but persists in Release builds (i.e. when NDEBUG is
+	defined)
 */
 
-__NORETURN extern void assert_fail(
+__NORETURN extern void sanity_check_fn(
 		const char *assertion, const char *file,
 		unsigned int line, const char *function);
 
-#define ASSERT(expr)\
-	((expr)\
-	? (void)(0)\
-	: assert_fail(#expr, __FILE__, __LINE__, __FUNCTION_NAME))
+#define SANITY_CHECK(expr) \
+	((expr) \
+	? (void)(0) \
+	: sanity_check_fn(#expr, __FILE__, __LINE__, __FUNCTION_NAME))
+
+#define sanity_check(expr) SANITY_CHECK(expr)
 
-#define assert(expr) ASSERT(expr)
 
 void debug_set_exception_handler();
 
diff --git a/src/environment.cpp b/src/environment.cpp
index 60a26e65f..f75e7a0b7 100644
--- a/src/environment.cpp
+++ b/src/environment.cpp
@@ -77,9 +77,9 @@ void Environment::addPlayer(Player *player)
 	*/
 	// If peer id is non-zero, it has to be unique.
 	if(player->peer_id != 0)
-		assert(getPlayer(player->peer_id) == NULL);
+		FATAL_ERROR_IF(getPlayer(player->peer_id) != NULL, "Peer id not unique");
 	// Name has to be unique.
-	assert(getPlayer(player->getName()) == NULL);
+	FATAL_ERROR_IF(getPlayer(player->getName()) != NULL, "Player name not unique");
 	// Add.
 	m_players.push_back(player);
 }
@@ -926,7 +926,7 @@ void ServerEnvironment::clearAllObjects()
 			i != loaded_blocks.end(); ++i) {
 		v3s16 p = *i;
 		MapBlock *block = m_map->getBlockNoCreateNoEx(p);
-		assert(block);
+		assert(block != NULL);
 		block->refGrab();
 	}
 
@@ -1295,7 +1295,7 @@ u16 getFreeServerActiveObjectId(
 
 u16 ServerEnvironment::addActiveObject(ServerActiveObject *object)
 {
-	assert(object);
+	assert(object);	// Pre-condition
 	m_added_objects++;
 	u16 id = addActiveObjectRaw(object, true, 0);
 	return id;
@@ -1473,7 +1473,7 @@ ActiveObjectMessage ServerEnvironment::getActiveObjectMessage()
 u16 ServerEnvironment::addActiveObjectRaw(ServerActiveObject *object,
 		bool set_changed, u32 dtime_s)
 {
-	assert(object);
+	assert(object); // Pre-condition
 	if(object->getId() == 0){
 		u16 new_id = getFreeServerActiveObjectId(m_active_objects);
 		if(new_id == 0)
@@ -2051,7 +2051,8 @@ void ClientEnvironment::addPlayer(Player *player)
 		It is a failure if player is local and there already is a local
 		player
 	*/
-	assert(!(player->isLocal() == true && getLocalPlayer() != NULL));
+	FATAL_ERROR_IF(player->isLocal() == true && getLocalPlayer() != NULL,
+		"Player is local but there is already a local player");
 
 	Environment::addPlayer(player);
 }
@@ -2439,7 +2440,7 @@ u16 getFreeClientActiveObjectId(
 
 u16 ClientEnvironment::addActiveObject(ClientActiveObject *object)
 {
-	assert(object);
+	assert(object); // Pre-condition
 	if(object->getId() == 0)
 	{
 		u16 new_id = getFreeClientActiveObjectId(m_active_objects);
diff --git a/src/fontengine.cpp b/src/fontengine.cpp
index 3b82a3c47..fa30b4038 100644
--- a/src/fontengine.cpp
+++ b/src/fontengine.cpp
@@ -55,9 +55,9 @@ FontEngine::FontEngine(Settings* main_settings, gui::IGUIEnvironment* env) :
 		m_default_size[i] = (FontMode) FONT_SIZE_UNSPECIFIED;
 	}
 
-	assert(m_settings != NULL);
-	assert(m_env != NULL);
-	assert(m_env->getSkin() != NULL);
+	assert(m_settings != NULL); // pre-condition
+	assert(m_env != NULL); // pre-condition
+	assert(m_env->getSkin() != NULL); // pre-condition
 
 	m_currentMode = FM_Simple;
 
@@ -172,7 +172,7 @@ unsigned int FontEngine::getTextHeight(unsigned int font_size, FontMode mode)
 	if (font == NULL) {
 		font = m_env->getSkin()->getFont();
 	}
-	assert(font != NULL);
+	FATAL_ERROR_IF(font == NULL, "Could not get skin font");
 
 	return font->getDimension(L"Some unimportant example String").Height;
 }
@@ -187,7 +187,7 @@ unsigned int FontEngine::getTextWidth(const std::wstring& text,
 	if (font == NULL) {
 		font = m_env->getSkin()->getFont();
 	}
-	assert(font != NULL);
+	FATAL_ERROR_IF(font == NULL, "Could not get font");
 
 	return font->getDimension(text.c_str()).Width;
 }
@@ -202,7 +202,7 @@ unsigned int FontEngine::getLineHeight(unsigned int font_size, FontMode mode)
 	if (font == NULL) {
 		font = m_env->getSkin()->getFont();
 	}
-	assert(font != NULL);
+	FATAL_ERROR_IF(font == NULL, "Could not get font");
 
 	return font->getDimension(L"Some unimportant example String").Height
 			+ font->getKerningHeight();
@@ -255,7 +255,7 @@ void FontEngine::updateSkin()
 
 	// If we did fail to create a font our own make irrlicht find a default one
 	font = m_env->getSkin()->getFont();
-	assert(font);
+	FATAL_ERROR_IF(font == NULL, "Could not create/get font");
 
 	u32 text_height = font->getDimension(L"Hello, world!").Height;
 	infostream << "text_height=" << text_height << std::endl;
@@ -355,7 +355,7 @@ void FontEngine::initFont(unsigned int basesize, FontMode mode)
 /** initialize a font without freetype */
 void FontEngine::initSimpleFont(unsigned int basesize, FontMode mode)
 {
-	assert((mode == FM_Simple) || (mode == FM_SimpleMono));
+	assert(mode == FM_Simple || mode == FM_SimpleMono); // pre-condition
 
 	std::string font_path = "";
 	if (mode == FM_Simple) {
diff --git a/src/game.cpp b/src/game.cpp
index be8d4e679..7b6d2a3c1 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -3112,7 +3112,7 @@ void Game::processClientEvents(CameraOrientation *cam, float *damage_flash)
 
 			u32 new_id = player->addHud(e);
 			//if this isn't true our huds aren't consistent
-			assert(new_id == id);
+			sanity_check(new_id == id);
 
 			delete event.hudadd.pos;
 			delete event.hudadd.name;
diff --git a/src/guiEngine.cpp b/src/guiEngine.cpp
index b45011c2c..dbb6fdf92 100644
--- a/src/guiEngine.cpp
+++ b/src/guiEngine.cpp
@@ -304,7 +304,7 @@ void GUIEngine::run()
 GUIEngine::~GUIEngine()
 {
 	video::IVideoDriver* driver = m_device->getVideoDriver();
-	assert(driver != 0);
+	FATAL_ERROR_IF(driver == 0, "Could not get video driver");
 
 	if(m_sound_manager != &dummySoundManager){
 		delete m_sound_manager;
@@ -514,7 +514,7 @@ bool GUIEngine::setTexture(texture_layer layer, std::string texturepath,
 		bool tile_image, unsigned int minsize)
 {
 	video::IVideoDriver* driver = m_device->getVideoDriver();
-	assert(driver != 0);
+	FATAL_ERROR_IF(driver == 0, "Could not get video driver");
 
 	if (m_textures[layer].texture != NULL)
 	{
diff --git a/src/guiFormSpecMenu.cpp b/src/guiFormSpecMenu.cpp
index 581da894b..300eaf80c 100644
--- a/src/guiFormSpecMenu.cpp
+++ b/src/guiFormSpecMenu.cpp
@@ -1973,7 +1973,7 @@ void GUIFormSpecMenu::regenerateGui(v2u32 screensize)
 	m_tooltip_element->setOverrideFont(m_font);
 
 	gui::IGUISkin* skin = Environment->getSkin();
-	assert(skin != NULL);
+	sanity_check(skin != NULL);
 	gui::IGUIFont *old_font = skin->getFont();
 	skin->setFont(m_font);
 
@@ -2217,9 +2217,9 @@ void GUIFormSpecMenu::drawSelectedItem()
 	video::IVideoDriver* driver = Environment->getVideoDriver();
 
 	Inventory *inv = m_invmgr->getInventory(m_selected_item->inventoryloc);
-	assert(inv);
+	sanity_check(inv);
 	InventoryList *list = inv->getList(m_selected_item->listname);
-	assert(list);
+	sanity_check(list);
 	ItemStack stack = list->getItem(m_selected_item->i);
 	stack.count = m_selected_amount;
 
@@ -2239,7 +2239,7 @@ void GUIFormSpecMenu::drawMenu()
 	}
 
 	gui::IGUISkin* skin = Environment->getSkin();
-	assert(skin != NULL);
+	sanity_check(skin != NULL);
 	gui::IGUIFont *old_font = skin->getFont();
 	skin->setFont(m_font);
 
@@ -2725,7 +2725,7 @@ bool GUIFormSpecMenu::preprocessEvent(const SEvent& event)
 		if (hovered && isMyChild(hovered) &&
 				hovered->getType() == gui::EGUIET_TAB_CONTROL) {
 			gui::IGUISkin* skin = Environment->getSkin();
-			assert(skin != NULL);
+			sanity_check(skin != NULL);
 			gui::IGUIFont *old_font = skin->getFont();
 			skin->setFont(m_font);
 			bool retval = hovered->OnEvent(event);
@@ -3013,7 +3013,7 @@ bool GUIFormSpecMenu::OnEvent(const SEvent& event)
 				break;
 				default:
 					//can't happen at all!
-					assert("reached a source line that can't ever been reached" == 0);
+					FATAL_ERROR("Reached a source line that can't ever been reached");
 					break;
 			}
 			if (current_keys_pending.key_enter && m_allowclose) {
@@ -3047,8 +3047,8 @@ bool GUIFormSpecMenu::OnEvent(const SEvent& event)
 
 		if(m_selected_item) {
 			inv_selected = m_invmgr->getInventory(m_selected_item->inventoryloc);
-			assert(inv_selected);
-			assert(inv_selected->getList(m_selected_item->listname) != NULL);
+			sanity_check(inv_selected);
+			sanity_check(inv_selected->getList(m_selected_item->listname) != NULL);
 		}
 
 		u32 s_count = 0;
diff --git a/src/guiKeyChangeMenu.cpp b/src/guiKeyChangeMenu.cpp
index 9b5a31d26..3ddb3f5d9 100644
--- a/src/guiKeyChangeMenu.cpp
+++ b/src/guiKeyChangeMenu.cpp
@@ -303,7 +303,7 @@ bool GUIKeyChangeMenu::OnEvent(const SEvent& event)
 
 		// But go on
 		{
-			key_setting *k=NULL;
+			key_setting *k = NULL;
 			for(size_t i = 0; i < key_settings.size(); i++)
 			{
 				if(key_settings.at(i)->id == activeKey)
@@ -312,7 +312,7 @@ bool GUIKeyChangeMenu::OnEvent(const SEvent& event)
 					break;
 				}
 			}
-			assert(k);
+			FATAL_ERROR_IF(k == NULL, "Key setting not found");
 			k->key = kp;
 			const wchar_t *text = wgettext(k->key.name());
 			k->button->setText(text);
@@ -364,7 +364,7 @@ bool GUIKeyChangeMenu::OnEvent(const SEvent& event)
 							break;
 						}
 					}
-					assert(k);
+					FATAL_ERROR_IF(k == NULL, "Key setting not found");
 
 					resetMenu();
 					shift_down = false;
diff --git a/src/httpfetch.cpp b/src/httpfetch.cpp
index e6886f652..40ad92da3 100644
--- a/src/httpfetch.cpp
+++ b/src/httpfetch.cpp
@@ -81,7 +81,7 @@ unsigned long httpfetch_caller_alloc()
 		}
 	}
 
-	assert("httpfetch_caller_alloc: ran out of caller IDs" == 0);
+	FATAL_ERROR("httpfetch_caller_alloc: ran out of caller IDs");
 	return discard;
 }
 
@@ -633,7 +633,7 @@ protected:
 			return NULL;
 		}
 
-		assert(m_all_ongoing.empty());
+		FATAL_ERROR_IF(!m_all_ongoing.empty(), "Expected empty");
 
 		while (!StopRequested()) {
 			BEGIN_DEBUG_EXCEPTION_HANDLER
@@ -714,7 +714,7 @@ void httpfetch_init(int parallel_limit)
 			<<std::endl;
 
 	CURLcode res = curl_global_init(CURL_GLOBAL_DEFAULT);
-	assert(res == CURLE_OK);
+	FATAL_ERROR_IF(res != CURLE_OK, "CURL init failed");
 
 	g_httpfetch_thread = new CurlFetchThread(parallel_limit);
 }
diff --git a/src/inventory.cpp b/src/inventory.cpp
index 3fa31965c..7941b3a2a 100644
--- a/src/inventory.cpp
+++ b/src/inventory.cpp
@@ -620,13 +620,13 @@ u32 InventoryList::getFreeSlots() const
 
 const ItemStack& InventoryList::getItem(u32 i) const
 {
-	assert(i < m_size);
+	assert(i < m_size); // Pre-condition
 	return m_items[i];
 }
 
 ItemStack& InventoryList::getItem(u32 i)
 {
-	assert(i < m_size);
+	assert(i < m_size); // Pre-condition
 	return m_items[i];
 }
 
@@ -643,7 +643,7 @@ ItemStack InventoryList::changeItem(u32 i, const ItemStack &newitem)
 
 void InventoryList::deleteItem(u32 i)
 {
-	assert(i < m_items.size());
+	assert(i < m_items.size()); // Pre-condition
 	m_items[i].clear();
 }
 
diff --git a/src/inventory.h b/src/inventory.h
index e4a97e1d3..faaa5ef95 100644
--- a/src/inventory.h
+++ b/src/inventory.h
@@ -71,7 +71,7 @@ struct ItemStack
 
 	void remove(u16 n)
 	{
-		assert(count >= n);
+		assert(count >= n); // Pre-condition
 		count -= n;
 		if(count == 0)
 			clear(); // reset name, wear and metadata too
diff --git a/src/inventorymanager.cpp b/src/inventorymanager.cpp
index ed18126d0..26cabc25f 100644
--- a/src/inventorymanager.cpp
+++ b/src/inventorymanager.cpp
@@ -62,7 +62,7 @@ void InventoryLocation::serialize(std::ostream &os) const
 		os<<"detached:"<<name;
 		break;
 	default:
-		assert(0);
+		FATAL_ERROR("Unhandled inventory location type");
 	}
 }
 
diff --git a/src/itemdef.cpp b/src/itemdef.cpp
index 381773bb4..65ba356f4 100644
--- a/src/itemdef.cpp
+++ b/src/itemdef.cpp
@@ -321,7 +321,7 @@ public:
 				<<name<<"\""<<std::endl;
 
 		// This is not thread-safe
-		assert(get_current_thread_id() == m_main_thread);
+		sanity_check(get_current_thread_id() == m_main_thread);
 
 		// Skip if already in cache
 		ClientCached *cc = NULL;
@@ -544,7 +544,7 @@ public:
 		verbosestream<<"ItemDefManager: registering \""<<def.name<<"\""<<std::endl;
 		// Ensure that the "" item (the hand) always has ToolCapabilities
 		if(def.name == "")
-			assert(def.tool_capabilities != NULL);
+			FATAL_ERROR_IF(!def.tool_capabilities, "Hand does not have ToolCapabilities");
 
 		if(m_item_definitions.count(def.name) == 0)
 			m_item_definitions[def.name] = new ItemDefinition(def);
diff --git a/src/keycode.cpp b/src/keycode.cpp
index 27d0b6d50..d9fc88934 100644
--- a/src/keycode.cpp
+++ b/src/keycode.cpp
@@ -263,7 +263,8 @@ KeyPress::KeyPress(const char *name)
 			m_name = name;
 			if (strlen(name) > 8 && strncmp(name, "KEY_KEY_", 8) == 0) {
 				int chars_read = mbtowc(&Char, name + 8, 1);
-				assert (chars_read == 1 && "unexpected multibyte character");
+
+				FATAL_ERROR_IF(chars_read != 1, "Unexpected multibyte character");
 			} else
 				Char = L'\0';
 			return;
@@ -275,7 +276,8 @@ KeyPress::KeyPress(const char *name)
 		try {
 			Key = keyname_to_keycode(m_name.c_str());
 			int chars_read = mbtowc(&Char, name, 1);
-			assert (chars_read == 1 && "unexpected multibyte character");
+
+			FATAL_ERROR_IF(chars_read != 1, "Unexpected multibyte character");
 			return;
 		} catch (UnknownKeycode &e) {};
 	}
@@ -285,7 +287,7 @@ KeyPress::KeyPress(const char *name)
 	Key = irr::KEY_KEY_CODES_COUNT;
 
 	int mbtowc_ret = mbtowc(&Char, name, 1);
-	assert (mbtowc_ret == 1 && "unexpected multibyte character");
+	FATAL_ERROR_IF(mbtowc_ret != 1, "Unexpected multibyte character");
 	m_name = name[0];
 }
 
diff --git a/src/localplayer.cpp b/src/localplayer.cpp
index cb183947a..55578422e 100644
--- a/src/localplayer.cpp
+++ b/src/localplayer.cpp
@@ -172,7 +172,7 @@ void LocalPlayer::move(f32 dtime, Environment *env, f32 pos_max_d,
 	f32 d = 0.15*BS;
 
 	// This should always apply, otherwise there are glitches
-	assert(d > pos_max_d);
+	sanity_check(d > pos_max_d);
 
 	// Maximum distance over border for sneaking
 	f32 sneak_max = BS*0.4;
diff --git a/src/localplayer.h b/src/localplayer.h
index 2a4a9dfc7..b60e156be 100644
--- a/src/localplayer.h
+++ b/src/localplayer.h
@@ -78,7 +78,7 @@ public:
 	}
 
 	void setCAO(GenericCAO* toset) {
-		assert( m_cao == NULL );
+		assert( m_cao == NULL ); // Pre-condition
 		m_cao = toset;
 	}
 
diff --git a/src/main.cpp b/src/main.cpp
index a01ddec93..d84a09f76 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -273,7 +273,7 @@ int main(int argc, char *argv[])
 	if (!game_configure(&game_params, cmd_args))
 		return 1;
 
-	assert(game_params.world_path != "");
+	sanity_check(game_params.world_path != "");
 
 	infostream << "Using commanded world path ["
 	           << game_params.world_path << "]" << std::endl;
@@ -549,7 +549,7 @@ static void startup_message()
 static bool read_config_file(const Settings &cmd_args)
 {
 	// Path of configuration file in use
-	assert(g_settings_path == "");	// Sanity check
+	sanity_check(g_settings_path == "");	// Sanity check
 
 	if (cmd_args.exists("config")) {
 		bool r = g_settings->readConfigFile(cmd_args.get("config").c_str());
@@ -748,7 +748,7 @@ static bool auto_select_world(GameParams *game_params)
 		           << world_path << "]" << std::endl;
 	}
 
-	assert(world_path != "");
+	assert(world_path != "");	// Post-condition
 	game_params->world_path = world_path;
 	return true;
 }
@@ -804,7 +804,7 @@ static bool determine_subgame(GameParams *game_params)
 {
 	SubgameSpec gamespec;
 
-	assert(game_params->world_path != "");	// pre-condition
+	assert(game_params->world_path != "");	// Pre-condition
 
 	verbosestream << _("Determining gameid/gamespec") << std::endl;
 	// If world doesn't exist
diff --git a/src/map.cpp b/src/map.cpp
index e80c82522..14a237c0a 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -767,8 +767,7 @@ void Map::updateLighting(enum LightBank bank,
 			}
 			else
 			{
-				// Invalid lighting bank
-				assert(0);
+				assert("Invalid lighting bank" == NULL);
 			}
 
 			/*infostream<<"Bottom for sunlight-propagated block ("
@@ -783,7 +782,7 @@ void Map::updateLighting(enum LightBank bank,
 			}
 			catch(InvalidPositionException &e)
 			{
-				assert(0);
+				FATAL_ERROR("Invalid position");
 			}
 
 		}
@@ -1220,7 +1219,7 @@ void Map::removeNodeAndUpdate(v3s16 p,
 			n.setLight(LIGHTBANK_DAY, 0, ndef);
 			setNode(p, n);
 		} else {
-			assert(0);
+			FATAL_ERROR("Invalid position");
 		}
 	}
 
@@ -2180,7 +2179,7 @@ bool ServerMap::initBlockMake(BlockMakeData *data, v3s16 blockpos)
 			v2s16 sectorpos(x, z);
 			// Sector metadata is loaded from disk if not already loaded.
 			ServerMapSector *sector = createSector(sectorpos);
-			assert(sector);
+			FATAL_ERROR_IF(sector == NULL, "createSector() failed");
 			(void) sector;
 
 			for(s16 y=blockpos_min.Y-extra_borders.Y;
@@ -2628,7 +2627,7 @@ MapBlock * ServerMap::createBlock(v3s16 p)
 		      lighting on blocks for them.
 	*/
 	ServerMapSector *sector;
-	try{
+	try {
 		sector = (ServerMapSector*)createSector(p2d);
 		assert(sector->getId() == MAPSECTOR_SERVER);
 	}
@@ -2861,9 +2860,10 @@ v2s16 ServerMap::getSectorPos(std::string dirname)
 	}
 	else
 	{
-		assert(false);
+		r = -1;
 	}
-	assert(r == 2);
+
+	FATAL_ERROR_IF(r != 2, "getSectorPos()");
 	v2s16 pos((s16)x, (s16)y);
 	return pos;
 }
@@ -3368,7 +3368,7 @@ void ServerMap::loadBlock(std::string sectordir, std::string blockfile,
 				<<"what()="<<e.what()
 				<<std::endl;
 				// Ignoring. A new one will be generated.
-		assert(0);
+		abort();
 
 		// TODO: Backup file; name is in fullpath.
 	}
@@ -3438,7 +3438,6 @@ void ServerMap::loadBlock(std::string *blob, v3s16 p3d, MapSector *sector, bool
 					<<"(ignore_world_load_errors)"<<std::endl;
 		} else {
 			throw SerializationError("Invalid block data in database");
-			//assert(0);
 		}
 	}
 }
diff --git a/src/map.h b/src/map.h
index a4fd8406b..325a02e60 100644
--- a/src/map.h
+++ b/src/map.h
@@ -263,15 +263,15 @@ public:
 	//bool updateChangedVisibleArea();
 
 	// Call these before and after saving of many blocks
-	virtual void beginSave() {return;};
-	virtual void endSave() {return;};
+	virtual void beginSave() { return; }
+	virtual void endSave() { return; }
 
-	virtual void save(ModifiedState save_level){assert(0);};
+	virtual void save(ModifiedState save_level) { FATAL_ERROR("FIXME"); }
 
 	// Server implements these.
 	// Client leaves them as no-op.
-	virtual bool saveBlock(MapBlock *block) { return false; };
-	virtual bool deleteBlock(v3s16 blockpos) { return false; };
+	virtual bool saveBlock(MapBlock *block) { return false; }
+	virtual bool deleteBlock(v3s16 blockpos) { return false; }
 
 	/*
 		Updates usage timers and unloads unused blocks and sectors.
diff --git a/src/mapblock.cpp b/src/mapblock.cpp
index a05b7a4da..ca80c39d7 100644
--- a/src/mapblock.cpp
+++ b/src/mapblock.cpp
@@ -521,7 +521,7 @@ void MapBlock::serialize(std::ostream &os, u8 version, bool disk)
 		throw SerializationError("ERROR: Not writing dummy block.");
 	}
 
-	assert(version >= SER_FMT_CLIENT_VER_LOWEST);
+	FATAL_ERROR_IF(version < SER_FMT_CLIENT_VER_LOWEST, "Serialize version error");
 
 	// First byte
 	u8 flags = 0;
diff --git a/src/mapblock.h b/src/mapblock.h
index 76ba94c34..3c0ae9cd7 100644
--- a/src/mapblock.h
+++ b/src/mapblock.h
@@ -140,7 +140,7 @@ public:
 	}
 	void unDummify()
 	{
-		assert(isDummy());
+		assert(isDummy()); // Pre-condition
 		reallocate();
 	}
 	
diff --git a/src/mapgen_singlenode.cpp b/src/mapgen_singlenode.cpp
index 5f81aba98..acf811dea 100644
--- a/src/mapgen_singlenode.cpp
+++ b/src/mapgen_singlenode.cpp
@@ -62,6 +62,7 @@ MapgenSinglenode::~MapgenSinglenode()
 
 void MapgenSinglenode::makeChunk(BlockMakeData *data)
 {
+	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
 	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
diff --git a/src/mapgen_v5.cpp b/src/mapgen_v5.cpp
index 34484c7e5..ffd164774 100644
--- a/src/mapgen_v5.cpp
+++ b/src/mapgen_v5.cpp
@@ -201,6 +201,7 @@ int MapgenV5::getGroundLevelAtPoint(v2s16 p)
 
 void MapgenV5::makeChunk(BlockMakeData *data)
 {
+	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
 	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
diff --git a/src/mapgen_v6.cpp b/src/mapgen_v6.cpp
index 8ea4cd21d..b7bfaef0c 100644
--- a/src/mapgen_v6.cpp
+++ b/src/mapgen_v6.cpp
@@ -430,6 +430,7 @@ u32 MapgenV6::get_blockseed(u64 seed, v3s16 p)
 
 void MapgenV6::makeChunk(BlockMakeData *data)
 {
+	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
 	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
diff --git a/src/mapgen_v7.cpp b/src/mapgen_v7.cpp
index 21ee967c6..923f85a0f 100644
--- a/src/mapgen_v7.cpp
+++ b/src/mapgen_v7.cpp
@@ -212,6 +212,7 @@ int MapgenV7::getGroundLevelAtPoint(v2s16 p)
 
 void MapgenV7::makeChunk(BlockMakeData *data)
 {
+	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
 	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
diff --git a/src/mapnode.cpp b/src/mapnode.cpp
index 44525b644..0335755e9 100644
--- a/src/mapnode.cpp
+++ b/src/mapnode.cpp
@@ -71,7 +71,7 @@ void MapNode::setLight(enum LightBank bank, u8 a_light, INodeDefManager *nodemgr
 		param1 |= (a_light & 0x0f)<<4;
 	}
 	else
-		assert(0);
+		assert("Invalid light bank" == NULL);
 }
 
 bool MapNode::isLightDayNightEq(INodeDefManager *nodemgr) const
@@ -516,8 +516,8 @@ void MapNode::serializeBulk(std::ostream &os, int version,
 	if(!ser_ver_supported(version))
 		throw VersionMismatchException("ERROR: MapNode format not supported");
 
-	assert(content_width == 2);
-	assert(params_width == 2);
+	sanity_check(content_width == 2);
+	sanity_check(params_width == 2);
 
 	// Can't do this anymore; we have 16-bit dynamically allocated node IDs
 	// in memory; conversion just won't work in this direction.
@@ -563,9 +563,10 @@ void MapNode::deSerializeBulk(std::istream &is, int version,
 	if(!ser_ver_supported(version))
 		throw VersionMismatchException("ERROR: MapNode format not supported");
 
-	assert(version >= 22);
-	assert(content_width == 1 || content_width == 2);
-	assert(params_width == 2);
+	if (version < 22
+			|| (content_width != 1 && content_width != 2)
+			|| params_width != 2)
+		FATAL_ERROR("Deserialize bulk node data error");
 
 	// Uncompress or read data
 	u32 len = nodecount * (content_width + params_width);
diff --git a/src/mapsector.cpp b/src/mapsector.cpp
index 7bc4bd3a3..3fe81dc90 100644
--- a/src/mapsector.cpp
+++ b/src/mapsector.cpp
@@ -85,7 +85,7 @@ MapBlock * MapSector::getBlockNoCreateNoEx(s16 y)
 
 MapBlock * MapSector::createBlankBlockNoInsert(s16 y)
 {
-	assert(getBlockBuffered(y) == NULL);
+	assert(getBlockBuffered(y) == NULL);	// Pre-condition
 
 	v3s16 blockpos_map(m_pos.X, y, m_pos.Y);
 	
diff --git a/src/mg_schematic.cpp b/src/mg_schematic.cpp
index a3404e2dc..a05e372e5 100644
--- a/src/mg_schematic.cpp
+++ b/src/mg_schematic.cpp
@@ -159,7 +159,7 @@ void Schematic::blitToVManip(v3s16 p, MMVManip *vm, Rotation rot,
 void Schematic::placeStructure(Map *map, v3s16 p, u32 flags, Rotation rot,
 	bool force_placement, INodeDefManager *ndef)
 {
-	assert(schemdata != NULL);
+	assert(schemdata != NULL); // Pre-condition
 	MMVManip *vm = new MMVManip(map);
 
 	if (rot == ROTATE_RAND)
diff --git a/src/network/connection.cpp b/src/network/connection.cpp
index b73981ccc..fb31a07f0 100644
--- a/src/network/connection.cpp
+++ b/src/network/connection.cpp
@@ -312,16 +312,16 @@ BufferedPacket ReliablePacketBuffer::popSeqnum(u16 seqnum)
 void ReliablePacketBuffer::insert(BufferedPacket &p,u16 next_expected)
 {
 	JMutexAutoLock listlock(m_list_mutex);
-	assert(p.data.getSize() >= BASE_HEADER_SIZE+3);
+	FATAL_ERROR_IF(p.data.getSize() < BASE_HEADER_SIZE+3, "Invalid data size");
 	u8 type = readU8(&p.data[BASE_HEADER_SIZE+0]);
-	assert(type == TYPE_RELIABLE);
+	sanity_check(type == TYPE_RELIABLE);
 	u16 seqnum = readU16(&p.data[BASE_HEADER_SIZE+1]);
 
-	assert(seqnum_in_window(seqnum,next_expected,MAX_RELIABLE_WINDOW_SIZE));
-	assert(seqnum != next_expected);
+	sanity_check(seqnum_in_window(seqnum, next_expected, MAX_RELIABLE_WINDOW_SIZE));
+	sanity_check(seqnum != next_expected);
 
 	++m_list_size;
-	assert(m_list_size <= SEQNUM_MAX+1);
+	sanity_check(m_list_size <= SEQNUM_MAX+1);	// FIXME: Handle the error?
 
 	// Find the right place for the packet and insert it there
 	// If list is empty, just add it
@@ -377,9 +377,9 @@ void ReliablePacketBuffer::insert(BufferedPacket &p,u16 next_expected)
 			throw IncomingDataCorruption("duplicated packet isn't same as original one");
 		}
 
-		assert(readU16(&(i->data[BASE_HEADER_SIZE+1])) == seqnum);
-		assert(i->data.getSize() == p.data.getSize());
-		assert(i->address == p.address);
+		sanity_check(readU16(&(i->data[BASE_HEADER_SIZE+1])) == seqnum);
+		sanity_check(i->data.getSize() == p.data.getSize());
+		sanity_check(i->address == p.address);
 
 		/* nothing to do this seems to be a resent packet */
 		/* for paranoia reason data should be compared */
@@ -449,9 +449,9 @@ SharedBuffer<u8> IncomingSplitBuffer::insert(BufferedPacket &p, bool reliable)
 {
 	JMutexAutoLock listlock(m_map_mutex);
 	u32 headersize = BASE_HEADER_SIZE + 7;
-	assert(p.data.getSize() >= headersize);
+	FATAL_ERROR_IF(p.data.getSize() < headersize, "Invalid data size");
 	u8 type = readU8(&p.data[BASE_HEADER_SIZE+0]);
-	assert(type == TYPE_SPLIT);
+	sanity_check(type == TYPE_SPLIT);
 	u16 seqnum = readU16(&p.data[BASE_HEADER_SIZE+1]);
 	u16 chunk_count = readU16(&p.data[BASE_HEADER_SIZE+3]);
 	u16 chunk_num = readU16(&p.data[BASE_HEADER_SIZE+5]);
@@ -898,7 +898,7 @@ void Peer::DecUseCount()
 {
 	{
 		JMutexAutoLock lock(m_exclusive_access_mutex);
-		assert(m_usage > 0);
+		sanity_check(m_usage > 0);
 		m_usage--;
 
 		if (!((m_pending_deletion) && (m_usage == 0)))
@@ -1085,7 +1085,7 @@ bool UDPPeer::processReliableSendCommand(
 							- BASE_HEADER_SIZE
 							- RELIABLE_HEADER_SIZE;
 
-	assert(c.data.getSize() < MAX_RELIABLE_WINDOW_SIZE*512);
+	sanity_check(c.data.getSize() < MAX_RELIABLE_WINDOW_SIZE*512);
 
 	std::list<SharedBuffer<u8> > originals;
 	u16 split_sequence_number = channels[c.channelnum].readNextSplitSeqNum();
@@ -1142,7 +1142,7 @@ bool UDPPeer::processReliableSendCommand(
 			channels[c.channelnum].queued_reliables.push(p);
 			pcount++;
 		}
-		assert(channels[c.channelnum].queued_reliables.size() < 0xFFFF);
+		sanity_check(channels[c.channelnum].queued_reliables.size() < 0xFFFF);
 		return true;
 	}
 	else {
@@ -1160,7 +1160,7 @@ bool UDPPeer::processReliableSendCommand(
 				= channels[c.channelnum].putBackSequenceNumber(
 					(initial_sequence_number+toadd.size() % (SEQNUM_MAX+1)));
 
-			assert(successfully_put_back_sequence_number);
+			FATAL_ERROR_IF(!successfully_put_back_sequence_number, "error");
 		}
 		LOG(dout_con<<m_connection->getDesc()
 				<< " Windowsize exceeded on reliable sending "
@@ -1212,13 +1212,13 @@ void UDPPeer::RunCommandQueues(
 
 u16 UDPPeer::getNextSplitSequenceNumber(u8 channel)
 {
-	assert(channel < CHANNEL_COUNT);
+	assert(channel < CHANNEL_COUNT); // Pre-condition
 	return channels[channel].readNextIncomingSeqNum();
 }
 
 void UDPPeer::setNextSplitSequenceNumber(u8 channel, u16 seqnum)
 {
-	assert(channel < CHANNEL_COUNT);
+	assert(channel < CHANNEL_COUNT); // Pre-condition
 	channels[channel].setNextSplitSeqNum(seqnum);
 }
 
@@ -1226,7 +1226,7 @@ SharedBuffer<u8> UDPPeer::addSpiltPacket(u8 channel,
 											BufferedPacket toadd,
 											bool reliable)
 {
-	assert(channel < CHANNEL_COUNT);
+	assert(channel < CHANNEL_COUNT); // Pre-condition
 	return channels[channel].incoming_splits.insert(toadd,reliable);
 }
 
@@ -1496,7 +1496,6 @@ void ConnectionSendThread::sendAsPacketReliable(BufferedPacket& p, Channel* chan
 		LOG(derr_con<<m_connection->getDesc()
 				<<"WARNING: Going to send a reliable packet"
 				<<" in outgoing buffer" <<std::endl);
-		//assert(0);
 	}
 
 	// Send the packet
@@ -1511,7 +1510,7 @@ bool ConnectionSendThread::rawSendAsPacket(u16 peer_id, u8 channelnum,
 		LOG(dout_con<<m_connection->getDesc()
 				<<" INFO: dropped packet for non existent peer_id: "
 				<< peer_id << std::endl);
-		assert(reliable && "trying to send raw packet reliable but no peer found!");
+		FATAL_ERROR_IF(!reliable, "Trying to send raw packet reliable but no peer found!");
 		return false;
 	}
 	Channel *channel = &(dynamic_cast<UDPPeer*>(&peer)->channels[channelnum]);
@@ -1582,7 +1581,7 @@ bool ConnectionSendThread::rawSendAsPacket(u16 peer_id, u8 channelnum,
 
 void ConnectionSendThread::processReliableCommand(ConnectionCommand &c)
 {
-	assert(c.reliable);
+	assert(c.reliable);  // Pre-condition
 
 	switch(c.type) {
 	case CONNCMD_NONE:
@@ -1626,7 +1625,7 @@ void ConnectionSendThread::processReliableCommand(ConnectionCommand &c)
 	case CONNCMD_CONNECT:
 	case CONNCMD_DISCONNECT:
 	case CONCMD_ACK:
-		assert("Got command that shouldn't be reliable as reliable command" == 0);
+		FATAL_ERROR("Got command that shouldn't be reliable as reliable command");
 	default:
 		LOG(dout_con<<m_connection->getDesc()
 				<<" Invalid reliable command type: " << c.type <<std::endl);
@@ -1636,7 +1635,7 @@ void ConnectionSendThread::processReliableCommand(ConnectionCommand &c)
 
 void ConnectionSendThread::processNonReliableCommand(ConnectionCommand &c)
 {
-	assert(!c.reliable);
+	assert(!c.reliable); // Pre-condition
 
 	switch(c.type) {
 	case CONNCMD_NONE:
@@ -1680,7 +1679,7 @@ void ConnectionSendThread::processNonReliableCommand(ConnectionCommand &c)
 		sendAsPacket(c.peer_id,c.channelnum,c.data,true);
 		return;
 	case CONCMD_CREATE_PEER:
-		assert("Got command that should be reliable as unreliable command" == 0);
+		FATAL_ERROR("Got command that should be reliable as unreliable command");
 	default:
 		LOG(dout_con<<m_connection->getDesc()
 				<<" Invalid command type: " << c.type <<std::endl);
@@ -1778,7 +1777,7 @@ void ConnectionSendThread::disconnect_peer(u16 peer_id)
 void ConnectionSendThread::send(u16 peer_id, u8 channelnum,
 		SharedBuffer<u8> data)
 {
-	assert(channelnum < CHANNEL_COUNT);
+	assert(channelnum < CHANNEL_COUNT); // Pre-condition
 
 	PeerHelper peer = m_connection->getPeerNoEx(peer_id);
 	if (!peer)
@@ -2331,7 +2330,7 @@ SharedBuffer<u8> ConnectionReceiveThread::processPacket(Channel *channel,
 
 	if (MAX_UDP_PEERS <= 65535 && peer_id >= MAX_UDP_PEERS) {
 		errorstream << "Something is wrong with peer_id" << std::endl;
-		assert(0);
+		FATAL_ERROR("");
 	}
 
 	if (type == TYPE_CONTROL)
@@ -2343,7 +2342,7 @@ SharedBuffer<u8> ConnectionReceiveThread::processPacket(Channel *channel,
 
 		if (controltype == CONTROLTYPE_ACK)
 		{
-			assert(channel != 0);
+			FATAL_ERROR_IF(channel == 0, "Invalid channel (0)");
 			if (packetdata.getSize() < 4)
 				throw InvalidIncomingDataException
 						("packetdata.getSize() < 4 (ACK header size)");
@@ -2511,7 +2510,7 @@ SharedBuffer<u8> ConnectionReceiveThread::processPacket(Channel *channel,
 	}
 	else if (type == TYPE_RELIABLE)
 	{
-		assert(channel != 0);
+		FATAL_ERROR_IF(channel == 0, "Invalid channel (0)");
 		// Recursive reliable packets not allowed
 		if (reliable)
 			throw InvalidIncomingDataException("Found nested reliable packets");
@@ -2635,10 +2634,7 @@ SharedBuffer<u8> ConnectionReceiveThread::processPacket(Channel *channel,
 	}
 
 	// We should never get here.
-	// If you get here, add an exception or a return to some of the
-	// above conditionals.
-	assert(0);
-	throw BaseException("Error in Channel::ProcessPacket()");
+	FATAL_ERROR("Invalid execution point");
 }
 
 /*
@@ -2724,7 +2720,7 @@ Connection::~Connection()
 /* Internal stuff */
 void Connection::putEvent(ConnectionEvent &e)
 {
-	assert(e.type != CONNEVENT_NONE);
+	assert(e.type != CONNEVENT_NONE); // Pre-condition
 	m_event_queue.push_back(e);
 }
 
@@ -2738,7 +2734,7 @@ PeerHelper Connection::getPeer(u16 peer_id)
 	}
 
 	// Error checking
-	assert(node->second->id == peer_id);
+	FATAL_ERROR_IF(node->second->id != peer_id, "Invalid peer id");
 
 	return PeerHelper(node->second);
 }
@@ -2753,7 +2749,7 @@ PeerHelper Connection::getPeerNoEx(u16 peer_id)
 	}
 
 	// Error checking
-	assert(node->second->id == peer_id);
+	FATAL_ERROR_IF(node->second->id != peer_id, "Invalid peer id");
 
 	return PeerHelper(node->second);
 }
@@ -2925,7 +2921,7 @@ u32 Connection::Receive(u16 &peer_id, SharedBuffer<u8> &data)
 void Connection::Send(u16 peer_id, u8 channelnum,
 		NetworkPacket* pkt, bool reliable)
 {
-	assert(channelnum < CHANNEL_COUNT);
+	assert(channelnum < CHANNEL_COUNT); // Pre-condition
 
 	ConnectionCommand c;
 
@@ -2955,9 +2951,7 @@ float Connection::getLocalStat(rate_stat_type type)
 {
 	PeerHelper peer = getPeerNoEx(PEER_ID_SERVER);
 
-	if (!peer) {
-		assert("Connection::getLocalStat we couldn't get our own peer? are you serious???" == 0);
-	}
+	FATAL_ERROR_IF(!peer, "Connection::getLocalStat we couldn't get our own peer? are you serious???");
 
 	float retval = 0.0;
 
@@ -2982,7 +2976,7 @@ float Connection::getLocalStat(rate_stat_type type)
 				retval += dynamic_cast<UDPPeer*>(&peer)->channels[j].getCurrentLossRateKB();
 				break;
 		default:
-			assert("Connection::getLocalStat Invalid stat type" == 0);
+			FATAL_ERROR("Connection::getLocalStat Invalid stat type");
 		}
 	}
 	return retval;
@@ -3075,7 +3069,7 @@ void Connection::DisconnectPeer(u16 peer_id)
 
 void Connection::sendAck(u16 peer_id, u8 channelnum, u16 seqnum)
 {
-	assert(channelnum < CHANNEL_COUNT);
+	assert(channelnum < CHANNEL_COUNT); // Pre-condition
 
 	LOG(dout_con<<getDesc()
 			<<" Queuing ACK command to peer_id: " << peer_id <<
diff --git a/src/network/connection.h b/src/network/connection.h
index 77d7edac0..33b7d0f7f 100644
--- a/src/network/connection.h
+++ b/src/network/connection.h
@@ -681,7 +681,7 @@ class Peer {
 
 		virtual ~Peer() {
 			JMutexAutoLock usage_lock(m_exclusive_access_mutex);
-			assert(m_usage == 0);
+			FATAL_ERROR_IF(m_usage != 0, "Reference counting failure");
 		};
 
 		// Unique id of the peer
@@ -926,7 +926,7 @@ public:
 	void Trigger();
 
 	void setParent(Connection* parent) {
-		assert(parent != NULL);
+		assert(parent != NULL); // Pre-condition
 		m_connection = parent;
 	}
 
@@ -980,7 +980,7 @@ public:
 	void * Thread       ();
 
 	void setParent(Connection* parent) {
-		assert(parent != NULL);
+		assert(parent != NULL); // Pre-condition
 		m_connection = parent;
 	}
 
diff --git a/src/network/packethandlers/client.cpp b/src/network/packethandlers/client.cpp
index 82f8b61b7..69f39d1f3 100644
--- a/src/network/packethandlers/client.cpp
+++ b/src/network/packethandlers/client.cpp
@@ -476,7 +476,7 @@ void Client::handleCommand_AnnounceMedia(NetworkPacket* pkt)
 
 	// Mesh update thread must be stopped while
 	// updating content definitions
-	assert(!m_mesh_update_thread.IsRunning());
+	sanity_check(!m_mesh_update_thread.IsRunning());
 
 	for (u16 i = 0; i < num_files; i++) {
 		std::string name, sha1_base64;
@@ -549,7 +549,7 @@ void Client::handleCommand_Media(NetworkPacket* pkt)
 
 	// Mesh update thread must be stopped while
 	// updating content definitions
-	assert(!m_mesh_update_thread.IsRunning());
+	sanity_check(!m_mesh_update_thread.IsRunning());
 
 	for (u32 i=0; i < num_files; i++) {
 		std::string name;
@@ -575,7 +575,7 @@ void Client::handleCommand_NodeDef(NetworkPacket* pkt)
 
 	// Mesh update thread must be stopped while
 	// updating content definitions
-	assert(!m_mesh_update_thread.IsRunning());
+	sanity_check(!m_mesh_update_thread.IsRunning());
 
 	// Decompress node definitions
 	std::string datastring(pkt->getString(0), pkt->getSize());
@@ -602,7 +602,7 @@ void Client::handleCommand_ItemDef(NetworkPacket* pkt)
 
 	// Mesh update thread must be stopped while
 	// updating content definitions
-	assert(!m_mesh_update_thread.IsRunning());
+	sanity_check(!m_mesh_update_thread.IsRunning());
 
 	// Decompress item definitions
 	std::string datastring(pkt->getString(0), pkt->getSize());
diff --git a/src/nodedef.cpp b/src/nodedef.cpp
index 6cf456e4d..a0dcf6b71 100644
--- a/src/nodedef.cpp
+++ b/src/nodedef.cpp
@@ -641,6 +641,7 @@ content_t CNodeDefManager::allocateId()
 // IWritableNodeDefManager
 content_t CNodeDefManager::set(const std::string &name, const ContentFeatures &def)
 {
+	// Pre-conditions
 	assert(name != "");
 	assert(name == def.name);
 
@@ -690,7 +691,7 @@ content_t CNodeDefManager::set(const std::string &name, const ContentFeatures &d
 
 content_t CNodeDefManager::allocateDummy(const std::string &name)
 {
-	assert(name != "");
+	assert(name != "");	// Pre-condition
 	ContentFeatures f;
 	f.name = name;
 	return set(name, f);
@@ -993,7 +994,9 @@ void CNodeDefManager::serialize(std::ostream &os, u16 protocol_version)
 		f->serialize(wrapper_os, protocol_version);
 		os2<<serializeString(wrapper_os.str());
 
-		assert(count + 1 > count); // must not overflow
+		// must not overflow
+		u16 next = count + 1;
+		FATAL_ERROR_IF(next < count, "Overflow");
 		count++;
 	}
 	writeU16(os, count);
diff --git a/src/noise.h b/src/noise.h
index 05c877b32..e59e73b23 100644
--- a/src/noise.h
+++ b/src/noise.h
@@ -58,12 +58,12 @@ public:
 		if (max-min > (PSEUDORANDOM_MAX + 1) / 10)
 		{
 			//dstream<<"WARNING: PseudoRandom::range: max > 32767"<<std::endl;
-			assert(0);
+			assert("Something wrong with random number" == NULL);
 		}
 		if(min > max)
 		{
-			assert(0);
-			return max;
+			assert("Something wrong with random number" == NULL);
+			//return max;
 		}
 		return (next()%(max-min+1))+min;
 	}
diff --git a/src/player.h b/src/player.h
index 435875233..4459b421a 100644
--- a/src/player.h
+++ b/src/player.h
@@ -216,7 +216,7 @@ public:
 	virtual PlayerSAO *getPlayerSAO()
 	{ return NULL; }
 	virtual void setPlayerSAO(PlayerSAO *sao)
-	{ assert(0); }
+	{ FATAL_ERROR("FIXME"); }
 
 	/*
 		serialize() writes a bunch of text that can contain
diff --git a/src/porting.cpp b/src/porting.cpp
index 8a685539b..6d0ab78c4 100644
--- a/src/porting.cpp
+++ b/src/porting.cpp
@@ -391,7 +391,7 @@ void initializePaths()
 	//TODO: Test this code
 	char buf[BUFSIZ];
 	uint32_t len = sizeof(buf);
-	assert(_NSGetExecutablePath(buf, &len) != -1);
+	FATAL_ERROR_IF(_NSGetExecutablePath(buf, &len) == -1, "");
 
 	pathRemoveFile(buf, '/');
 
@@ -411,7 +411,7 @@ void initializePaths()
 	mib[1] = KERN_PROC;
 	mib[2] = KERN_PROC_PATHNAME;
 	mib[3] = -1;
-	assert(sysctl(mib, 4, buf, &len, NULL, 0) != -1);
+	FATAL_ERROR_IF(sysctl(mib, 4, buf, &len, NULL, 0) == -1, "");
 
 	pathRemoveFile(buf, '/');
 
@@ -446,13 +446,13 @@ void initializePaths()
 	*/
 	#if defined(_WIN32)
 
-	const DWORD buflen = 1000;
+	const DWORD buflen = 1000; // FIXME: Surely there is a better way to do this
 	char buf[buflen];
 	DWORD len;
 
 	// Find path of executable and set path_share relative to it
 	len = GetModuleFileName(GetModuleHandle(NULL), buf, buflen);
-	assert(len < buflen);
+	FATAL_ERROR_IF(len >= buflen, "Overlow");
 	pathRemoveFile(buf, '\\');
 
 	// Use ".\bin\.."
@@ -460,7 +460,7 @@ void initializePaths()
 
 	// Use "C:\Documents and Settings\user\Application Data\<PROJECT_NAME>"
 	len = GetEnvironmentVariable("APPDATA", buf, buflen);
-	assert(len < buflen);
+	FATAL_ERROR_IF(len >= buflen, "Overlow");
 	path_user = std::string(buf) + DIR_DELIM + PROJECT_NAME;
 
 	/*
@@ -476,7 +476,7 @@ void initializePaths()
 		if (readlink("/proc/self/exe", buf, BUFSIZ-1) == -1) {
 			errorstream << "Unable to read bindir "<< std::endl;
 #ifndef __ANDROID__
-			assert("Unable to read bindir" == 0);
+			FATAL_ERROR("Unable to read bindir");
 #endif
 		} else {
 			pathRemoveFile(buf, '/');
diff --git a/src/script/common/c_internal.cpp b/src/script/common/c_internal.cpp
index f811dd5d3..61248534c 100644
--- a/src/script/common/c_internal.cpp
+++ b/src/script/common/c_internal.cpp
@@ -87,7 +87,7 @@ void script_error(lua_State *L)
 //     computed depending on mode
 void script_run_callbacks(lua_State *L, int nargs, RunCallbacksMode mode)
 {
-	assert(lua_gettop(L) >= nargs + 1);
+	FATAL_ERROR_IF(lua_gettop(L) < nargs + 1, "Not enough arguments");
 
 	// Insert error handler
 	lua_pushcfunction(L, script_error_handler);
@@ -136,9 +136,7 @@ void log_deprecated(lua_State *L, std::string message)
 		if (L != NULL) {
 			script_error(L);
 		} else {
-			/* As of april 2014 assert is not optimized to nop in release builds
-			 * therefore this is correct. */
-			assert("Can't do a scripterror for this deprecated message, so exit completely!");
+			FATAL_ERROR("Can't do a scripterror for this deprecated message, so exit completely!");
 		}
 	}
 
diff --git a/src/script/cpp_api/s_async.cpp b/src/script/cpp_api/s_async.cpp
index de1ebc07b..eb1a2923a 100644
--- a/src/script/cpp_api/s_async.cpp
+++ b/src/script/cpp_api/s_async.cpp
@@ -155,7 +155,7 @@ void AsyncEngine::step(lua_State *L, int errorhandler)
 		lua_getfield(L, -1, "async_event_handler");
 
 		if (lua_isnil(L, -1)) {
-			assert("Async event handler does not exist!" == 0);
+			FATAL_ERROR("Async event handler does not exist!");
 		}
 
 		luaL_checktype(L, -1, LUA_TFUNCTION);
@@ -237,7 +237,7 @@ AsyncWorkerThread::AsyncWorkerThread(AsyncEngine* jobDispatcher,
 /******************************************************************************/
 AsyncWorkerThread::~AsyncWorkerThread()
 {
-	assert(IsRunning() == false);
+	sanity_check(IsRunning() == false);
 }
 
 /******************************************************************************/
diff --git a/src/script/cpp_api/s_base.cpp b/src/script/cpp_api/s_base.cpp
index 1f96373dc..71473d215 100644
--- a/src/script/cpp_api/s_base.cpp
+++ b/src/script/cpp_api/s_base.cpp
@@ -72,7 +72,7 @@ ScriptApiBase::ScriptApiBase()
 	#endif
 
 	m_luastack = luaL_newstate();
-	assert(m_luastack);
+	FATAL_ERROR_IF(!m_luastack, "luaL_newstate() failed");
 
 	luaL_openlibs(m_luastack);
 
diff --git a/src/script/lua_api/l_env.cpp b/src/script/lua_api/l_env.cpp
index 1f1d8bffa..840c34595 100644
--- a/src/script/lua_api/l_env.cpp
+++ b/src/script/lua_api/l_env.cpp
@@ -49,7 +49,7 @@ void LuaABM::trigger(ServerEnvironment *env, v3s16 p, MapNode n,
 	scriptIface->realityCheck();
 
 	lua_State *L = scriptIface->getStack();
-	assert(lua_checkstack(L, 20));
+	sanity_check(lua_checkstack(L, 20));
 	StackUnroller stack_unroller(L);
 
 	lua_pushcfunction(L, script_error_handler);
@@ -65,7 +65,7 @@ void LuaABM::trigger(ServerEnvironment *env, v3s16 p, MapNode n,
 	lua_pushnumber(L, m_id);
 	lua_gettable(L, -2);
 	if(lua_isnil(L, -1))
-		assert(0);
+		FATAL_ERROR("");
 	lua_remove(L, -2); // Remove registered_abms
 
 	// Call action
@@ -459,7 +459,7 @@ int ModApiEnvMod::l_set_timeofday(lua_State *L)
 
 	// Do it
 	float timeofday_f = luaL_checknumber(L, 1);
-	assert(timeofday_f >= 0.0 && timeofday_f <= 1.0);
+	sanity_check(timeofday_f >= 0.0 && timeofday_f <= 1.0);
 	int timeofday_mh = (int)(timeofday_f * 24000.0);
 	// This should be set directly in the environment but currently
 	// such changes aren't immediately sent to the clients, so call
diff --git a/src/script/lua_api/l_mainmenu.cpp b/src/script/lua_api/l_mainmenu.cpp
index 2bed2a255..e6fcdcf83 100644
--- a/src/script/lua_api/l_mainmenu.cpp
+++ b/src/script/lua_api/l_mainmenu.cpp
@@ -90,7 +90,7 @@ int ModApiMainMenu::getBoolData(lua_State *L, std::string name,bool& valid)
 int ModApiMainMenu::l_update_formspec(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	if (engine->m_startgame)
 		return 0;
@@ -109,7 +109,7 @@ int ModApiMainMenu::l_update_formspec(lua_State *L)
 int ModApiMainMenu::l_start(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	//update c++ gamedata from lua table
 
@@ -134,7 +134,7 @@ int ModApiMainMenu::l_start(lua_State *L)
 int ModApiMainMenu::l_close(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	engine->m_kill = true;
 	return 0;
@@ -144,7 +144,7 @@ int ModApiMainMenu::l_close(lua_State *L)
 int ModApiMainMenu::l_set_background(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	std::string backgroundlevel(luaL_checkstring(L, 1));
 	std::string texturename(luaL_checkstring(L, 2));
@@ -189,7 +189,7 @@ int ModApiMainMenu::l_set_background(lua_State *L)
 int ModApiMainMenu::l_set_clouds(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	bool value = lua_toboolean(L,1);
 
@@ -209,7 +209,7 @@ int ModApiMainMenu::l_get_textlist_index(lua_State *L)
 int ModApiMainMenu::l_get_table_index(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	std::wstring tablename(narrow_to_wide(luaL_checkstring(L, 1)));
 	GUITable *table = engine->m_menu->getTable(tablename);
@@ -617,7 +617,7 @@ int ModApiMainMenu::l_delete_favorite(lua_State *L)
 int ModApiMainMenu::l_show_keys_menu(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	GUIKeyChangeMenu *kmenu
 		= new GUIKeyChangeMenu(	engine->m_device->getGUIEnvironment(),
@@ -692,7 +692,7 @@ int ModApiMainMenu::l_delete_world(lua_State *L)
 int ModApiMainMenu::l_set_topleft_text(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	std::string text = "";
 
@@ -843,7 +843,7 @@ int ModApiMainMenu::l_copy_dir(lua_State *L)
 int ModApiMainMenu::l_extract_zip(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);(engine != 0);
 
 	const char *zipfile	= luaL_checkstring(L, 1);
 	const char *destination	= luaL_checkstring(L, 2);
@@ -860,7 +860,7 @@ int ModApiMainMenu::l_extract_zip(lua_State *L)
 			return 1;
 		}
 
-		assert(fs->getFileArchiveCount() > 0);
+		sanity_check(fs->getFileArchiveCount() > 0);
 
 		/**********************************************************************/
 		/* WARNING this is not threadsafe!!                                   */
@@ -931,7 +931,7 @@ int ModApiMainMenu::l_extract_zip(lua_State *L)
 int ModApiMainMenu::l_get_mainmenu_path(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	lua_pushstring(L,engine->getScriptDir().c_str());
 	return 1;
@@ -963,7 +963,7 @@ bool ModApiMainMenu::isMinetestPath(std::string path)
 int ModApiMainMenu::l_show_file_open_dialog(lua_State *L)
 {
 	GUIEngine* engine = getGuiEngine(L);
-	assert(engine != 0);
+	sanity_check(engine != NULL);
 
 	const char *formname= luaL_checkstring(L, 1);
 	const char *title	= luaL_checkstring(L, 2);
@@ -1118,8 +1118,8 @@ int ModApiMainMenu::l_do_async_callback(lua_State *L)
 
 	const char* serialized_param_raw = luaL_checklstring(L, 2, &param_length);
 
-	assert(serialized_func_raw != NULL);
-	assert(serialized_param_raw != NULL);
+	sanity_check(serialized_func_raw != NULL);
+	sanity_check(serialized_param_raw != NULL);
 
 	std::string serialized_func = std::string(serialized_func_raw, func_length);
 	std::string serialized_param = std::string(serialized_param_raw, param_length);
diff --git a/src/server.cpp b/src/server.cpp
index 09884f1bc..de23820dd 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -1306,7 +1306,7 @@ Inventory* Server::getInventory(const InventoryLocation &loc)
 	}
 		break;
 	default:
-		assert(0);
+		sanity_check(false); // abort
 		break;
 	}
 	return NULL;
@@ -1345,7 +1345,7 @@ void Server::setInventoryModified(const InventoryLocation &loc)
 	}
 		break;
 	default:
-		assert(0);
+		sanity_check(false); // abort
 		break;
 	}
 }
@@ -1454,7 +1454,7 @@ void Server::handlePeerChanges()
 			break;
 
 		default:
-			assert("Invalid peer change event received!" == 0);
+			FATAL_ERROR("Invalid peer change event received!");
 			break;
 		}
 	}
@@ -2637,8 +2637,8 @@ void Server::UpdateCrafting(Player* player)
 
 	// Put the new preview in
 	InventoryList *plist = player->inventory.getList("craftpreview");
-	assert(plist);
-	assert(plist->getSize() >= 1);
+	sanity_check(plist);
+	sanity_check(plist->getSize() >= 1);
 	plist->changeItem(0, preview);
 }
 
@@ -3026,7 +3026,7 @@ Inventory* Server::createDetachedInventory(const std::string &name)
 		infostream<<"Server creating detached inventory \""<<name<<"\""<<std::endl;
 	}
 	Inventory *inv = new Inventory(m_itemdef);
-	assert(inv);
+	sanity_check(inv);
 	m_detached_inventories[name] = inv;
 	//TODO find a better way to do this
 	sendDetachedInventory(name,PEER_ID_INEXISTENT);
diff --git a/src/settings.cpp b/src/settings.cpp
index 7339af62b..594b8944d 100644
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -264,7 +264,7 @@ bool Settings::updateConfigObject(std::istream &is, std::ostream &os,
 			it = m_settings.find(name);
 			if (it != m_settings.end() && it->second.is_group) {
 				os << line << "\n";
-				assert(it->second.group != NULL);
+				sanity_check(it->second.group != NULL);
 				was_modified |= it->second.group->updateConfigObject(is, os,
 					"}", tab_depth + 1);
 			} else {
diff --git a/src/shader.cpp b/src/shader.cpp
index 8c572ed49..8a5fd417b 100644
--- a/src/shader.cpp
+++ b/src/shader.cpp
@@ -196,7 +196,7 @@ public:
 	virtual void OnSetConstants(video::IMaterialRendererServices *services, s32 userData)
 	{
 		video::IVideoDriver *driver = services->getVideoDriver();
-		assert(driver);
+		sanity_check(driver != NULL);
 
 		bool is_highlevel = userData;
 
@@ -219,7 +219,7 @@ public:
 			bool is_highlevel)
 	{
 		video::IVideoDriver *driver = services->getVideoDriver();
-		assert(driver);
+		sanity_check(driver);
 
 		// set inverted world matrix
 		core::matrix4 invWorld = driver->getTransform(video::ETS_WORLD);
@@ -364,7 +364,7 @@ void load_shaders(std::string name, SourceShaderCache *sourcecache,
 ShaderSource::ShaderSource(IrrlichtDevice *device):
 		m_device(device)
 {
-	assert(m_device);
+	assert(m_device); // Pre-condition
 
 	m_shader_callback = new ShaderCallback(this, "default");
 
@@ -505,7 +505,7 @@ void ShaderSource::insertSourceShader(const std::string &name_of_shader,
 			"name_of_shader=\""<<name_of_shader<<"\", "
 			"filename=\""<<filename<<"\""<<std::endl;*/
 
-	assert(get_current_thread_id() == m_main_thread);
+	sanity_check(get_current_thread_id() == m_main_thread);
 
 	m_sourcecache.insert(name_of_shader, filename, program, true);
 }
@@ -578,7 +578,7 @@ ShaderInfo generate_shader(std::string name, u8 material_type, u8 drawtype,
 		return shaderinfo;
 
 	video::IVideoDriver* driver = device->getVideoDriver();
-	assert(driver);
+	sanity_check(driver);
 
 	video::IGPUProgrammingServices *gpu = driver->getGPUProgrammingServices();
 	if(!gpu){
diff --git a/src/sound_openal.cpp b/src/sound_openal.cpp
index b2b424a19..cb4c7b581 100644
--- a/src/sound_openal.cpp
+++ b/src/sound_openal.cpp
@@ -37,10 +37,10 @@ with this program; ifnot, write to the Free Software Foundation, Inc.,
 	#include <AL/alext.h>
 #endif
 #include <vorbis/vorbisfile.h>
+#include <assert.h>
 #include "log.h"
 #include "filesys.h"
 #include "util/numeric.h" // myrand()
-#include "debug.h" // assert()
 #include "porting.h"
 #include <map>
 #include <vector>
diff --git a/src/staticobject.h b/src/staticobject.h
index 4918a1466..95a1b945e 100644
--- a/src/staticobject.h
+++ b/src/staticobject.h
@@ -68,8 +68,7 @@ public:
 			{
 				dstream<<"ERROR: StaticObjectList::insert(): "
 						<<"id already exists"<<std::endl;
-				assert(0);
-				return;
+				FATAL_ERROR("StaticObjectList::insert()");
 			}
 			m_active[id] = obj;
 		}
@@ -77,7 +76,7 @@ public:
 
 	void remove(u16 id)
 	{
-		assert(id != 0);
+		assert(id != 0); // Pre-condition
 		if(m_active.find(id) == m_active.end())
 		{
 			dstream<<"WARNING: StaticObjectList::remove(): id="<<id
diff --git a/src/test.cpp b/src/test.cpp
index 350cab127..7b82a2c31 100644
--- a/src/test.cpp
+++ b/src/test.cpp
@@ -2115,8 +2115,6 @@ struct TestConnection: public TestBase
 		UASSERT(hand_client.last_id == 1);
 		UASSERT(hand_server.count == 1);
 		UASSERT(hand_server.last_id == 2);
-
-		//assert(0);
 	}
 };
 
diff --git a/src/util/serialize.cpp b/src/util/serialize.cpp
index 8a108a0ff..659e816b0 100644
--- a/src/util/serialize.cpp
+++ b/src/util/serialize.cpp
@@ -31,7 +31,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 // Creates a string with the length as the first two bytes
 std::string serializeString(const std::string &plain)
 {
-	//assert(plain.size() <= 65535);
 	if(plain.size() > 65535)
 		throw SerializationError("String too long for serializeString");
 	char buf[2];
@@ -45,7 +44,6 @@ std::string serializeString(const std::string &plain)
 // Creates a string with the length as the first two bytes from wide string
 std::string serializeWideString(const std::wstring &plain)
 {
-	//assert(plain.size() <= 65535);
 	if(plain.size() > 65535)
 		throw SerializationError("String too long for serializeString");
 	char buf[2];
diff --git a/src/util/string.cpp b/src/util/string.cpp
index 651293bfe..02a0586e7 100644
--- a/src/util/string.cpp
+++ b/src/util/string.cpp
@@ -320,7 +320,7 @@ char *mystrtok_r(char *s, const char *sep, char **lasts)
 		}
 		t++;
 	}
-	
+
 	*lasts = t;
 	return s;
 }
@@ -329,15 +329,15 @@ u64 read_seed(const char *str)
 {
 	char *endptr;
 	u64 num;
-	
+
 	if (str[0] == '0' && str[1] == 'x')
 		num = strtoull(str, &endptr, 16);
 	else
 		num = strtoull(str, &endptr, 10);
-		
+
 	if (*endptr)
 		num = murmur_hash_64_ua(str, (int)strlen(str), 0x1337);
-		
+
 	return num;
 }
 
@@ -614,4 +614,3 @@ void str_replace(std::string &str, char from, char to)
 {
 	std::replace(str.begin(), str.end(), from, to);
 }
-
diff --git a/src/voxel.h b/src/voxel.h
index 054644889..58ad39be4 100644
--- a/src/voxel.h
+++ b/src/voxel.h
@@ -213,7 +213,7 @@ public:
 			return;
 		}
 
-		assert(contains(a));
+		assert(contains(a));	// pre-condition
 
 		// Take back area, XY inclusive
 		{
diff --git a/src/wieldmesh.cpp b/src/wieldmesh.cpp
index a2be55544..c1a898c1b 100644
--- a/src/wieldmesh.cpp
+++ b/src/wieldmesh.cpp
@@ -170,7 +170,7 @@ public:
 		if (it == m_extrusion_meshes.end()) {
 			// no viable resolution found; use largest one
 			it = m_extrusion_meshes.find(MAX_EXTRUSION_MESH_RESOLUTION);
-			assert(it != m_extrusion_meshes.end());
+			sanity_check(it != m_extrusion_meshes.end());
 		}
 
 		scene::IMesh *mesh = it->second;
@@ -231,7 +231,7 @@ WieldMeshSceneNode::WieldMeshSceneNode(
 
 WieldMeshSceneNode::~WieldMeshSceneNode()
 {
-	assert(g_extrusion_mesh_cache);
+	sanity_check(g_extrusion_mesh_cache);
 	if (g_extrusion_mesh_cache->drop())
 		g_extrusion_mesh_cache = NULL;
 }