diff --git a/irr/src/CNullDriver.cpp b/irr/src/CNullDriver.cpp
index 46a2d9f7b..acce8383b 100644
--- a/irr/src/CNullDriver.cpp
+++ b/irr/src/CNullDriver.cpp
@@ -936,9 +936,10 @@ void CNullDriver::setTextureCreationFlag(E_TEXTURE_CREATION_FLAG flag, bool enab
 		setTextureCreationFlag(ETCF_OPTIMIZED_FOR_SPEED, false);
 	}
 
-	// set flag
-	TextureCreationFlags = (TextureCreationFlags & (~flag)) |
-						   ((((u32)!enabled) - 1) & flag);
+	if (enabled)
+		TextureCreationFlags |= flag;
+	else
+		TextureCreationFlags &= ~flag;
 }
 
 //! Returns if a texture creation flag is enabled or disabled.
diff --git a/irr/src/OpenGL/Driver.cpp b/irr/src/OpenGL/Driver.cpp
index 4f3ac627a..4b85b1345 100644
--- a/irr/src/OpenGL/Driver.cpp
+++ b/irr/src/OpenGL/Driver.cpp
@@ -144,7 +144,7 @@ void COpenGL3DriverBase::debugCb(GLenum source, GLenum type, GLuint id, GLenum s
 		ll = ELL_ERROR;
 	else if (severity == GL_DEBUG_SEVERITY_MEDIUM)
 		ll = ELL_WARNING;
-	char buf[256];
+	char buf[300];
 	snprintf_irr(buf, sizeof(buf), "%04x %04x %.*s", source, type, length, message);
 	os::Printer::log("GL", buf, ll);
 }
@@ -700,15 +700,7 @@ void COpenGL3DriverBase::drawVertexPrimitiveList(const void *vertices, u32 verte
 		break;
 	}
 	case (EIT_32BIT): {
-#ifdef GL_OES_element_index_uint
-#ifndef GL_UNSIGNED_INT
-#define GL_UNSIGNED_INT 0x1405
-#endif
-		if (FeatureAvailable[COGLESCoreExtensionHandler::IRR_GL_OES_element_index_uint])
-			indexSize = GL_UNSIGNED_INT;
-		else
-#endif
-			indexSize = GL_UNSIGNED_SHORT;
+		indexSize = GL_UNSIGNED_INT;
 		break;
 	}
 	}
@@ -1683,7 +1675,7 @@ ITexture *COpenGL3DriverBase::addRenderTargetTextureCubemap(const irr::u32 sideL
 //! Returns the maximum amount of primitives
 u32 COpenGL3DriverBase::getMaximalPrimitiveCount() const
 {
-	return 65535;
+	return Version.Spec == OpenGLSpec::ES ? 65535 : 0x7fffffff;
 }
 
 bool COpenGL3DriverBase::setRenderTargetEx(IRenderTarget *target, u16 clearFlag, SColor clearColor, f32 clearDepth, u8 clearStencil)
diff --git a/irr/src/OpenGL/MaterialRenderer.cpp b/irr/src/OpenGL/MaterialRenderer.cpp
index 3c32ba318..d5bf9004a 100644
--- a/irr/src/OpenGL/MaterialRenderer.cpp
+++ b/irr/src/OpenGL/MaterialRenderer.cpp
@@ -411,7 +411,7 @@ bool COpenGL3MaterialRenderer::setPixelShaderConstant(s32 index, const s32 *ints
 
 bool COpenGL3MaterialRenderer::setPixelShaderConstant(s32 index, const u32 *ints, int count)
 {
-	os::Printer::log("Unsigned int support needs at least GLES 3.0", ELL_WARNING);
+	os::Printer::log("Unsigned int support is unimplemented", ELL_WARNING);
 	return false;
 }
 
diff --git a/irr/src/OpenGL3/Driver.cpp b/irr/src/OpenGL3/Driver.cpp
index a58e1542f..ac0816445 100644
--- a/irr/src/OpenGL3/Driver.cpp
+++ b/irr/src/OpenGL3/Driver.cpp
@@ -4,6 +4,7 @@
 
 #include "Driver.h"
 #include <cassert>
+#include <stdexcept>
 #include "mt_opengl.h"
 
 namespace irr
@@ -18,7 +19,7 @@ E_DRIVER_TYPE COpenGL3Driver::getDriverType() const
 
 OpenGLVersion COpenGL3Driver::getVersionFromOpenGL() const
 {
-	GLint major, minor, profile;
+	GLint major = 0, minor = 0, profile = 0;
 	GL.GetIntegerv(GL_MAJOR_VERSION, &major);
 	GL.GetIntegerv(GL_MINOR_VERSION, &minor);
 	GL.GetIntegerv(GL_CONTEXT_PROFILE_MASK, &profile);
@@ -35,18 +36,21 @@ OpenGLVersion COpenGL3Driver::getVersionFromOpenGL() const
 void COpenGL3Driver::initFeatures()
 {
 	if (Version.Spec != OpenGLSpec::Compat) {
-		os::Printer::log("OpenGL 3 driver requires Compatibility Mode", ELL_ERROR);
-		throw std::exception();
+		auto msg = "OpenGL 3 driver requires Compatibility context";
+		os::Printer::log(msg, ELL_ERROR);
+		throw std::runtime_error(msg);
 	}
 	if (!isVersionAtLeast(3, 2)) {
-		os::Printer::log("OpenGL 3 driver requires OpenGL >= 3.2 ", ELL_ERROR);
-		throw std::exception();
+		auto msg = "OpenGL 3 driver requires OpenGL >= 3.2";
+		os::Printer::log(msg, ELL_ERROR);
+		throw std::runtime_error(msg);
 	}
 	initExtensions();
 
 	TextureFormats[ECF_A1R5G5B5] = {GL_RGB5_A1, GL_BGRA, GL_UNSIGNED_SHORT_1_5_5_5_REV}; // WARNING: may not be renderable
 	TextureFormats[ECF_R5G6B5] = {GL_RGB, GL_RGB, GL_UNSIGNED_SHORT_5_6_5};              // GL_RGB565 is an extension until 4.1
 	TextureFormats[ECF_R8G8B8] = {GL_RGB8, GL_RGB, GL_UNSIGNED_BYTE};                    // WARNING: may not be renderable
+	// FIXME: shouldn't this simply be GL_UNSIGNED_BYTE?
 	TextureFormats[ECF_A8R8G8B8] = {GL_RGBA8, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV};
 	TextureFormats[ECF_R16F] = {GL_R16F, GL_RED, GL_HALF_FLOAT};
 	TextureFormats[ECF_G16R16F] = {GL_RG16F, GL_RG, GL_HALF_FLOAT};
diff --git a/irr/src/OpenGLES2/Driver.cpp b/irr/src/OpenGLES2/Driver.cpp
index e423abb2e..430be736d 100644
--- a/irr/src/OpenGLES2/Driver.cpp
+++ b/irr/src/OpenGLES2/Driver.cpp
@@ -3,8 +3,10 @@
 // For conditions of distribution and use, see copyright notice in Irrlicht.h
 
 #include "Driver.h"
+#include <stdexcept>
 #include <cassert>
-#include <CColorConverter.h>
+#include "mt_opengl.h"
+#include "CColorConverter.h"
 
 namespace irr
 {
@@ -19,7 +21,7 @@ E_DRIVER_TYPE COpenGLES2Driver::getDriverType() const
 OpenGLVersion COpenGLES2Driver::getVersionFromOpenGL() const
 {
 	auto version_string = reinterpret_cast<const char *>(GL.GetString(GL_VERSION));
-	int major, minor;
+	int major = 0, minor = 0;
 	if (sscanf(version_string, "OpenGL ES %d.%d", &major, &minor) != 2) {
 		os::Printer::log("Failed to parse OpenGL ES version string", version_string, ELL_ERROR);
 		return {OpenGLSpec::ES, 0, 0, 0};
@@ -29,8 +31,16 @@ OpenGLVersion COpenGLES2Driver::getVersionFromOpenGL() const
 
 void COpenGLES2Driver::initFeatures()
 {
-	assert(Version.Spec == OpenGLSpec::ES);
-	assert(Version.Major >= 2);
+	if (Version.Spec != OpenGLSpec::ES) {
+		auto msg = "Context isn't OpenGL ES";
+		os::Printer::log(msg, ELL_ERROR);
+		throw std::runtime_error(msg);
+	}
+	if (!isVersionAtLeast(2, 0)) {
+		auto msg = "Open GL ES 2.0 is required";
+		os::Printer::log(msg, ELL_ERROR);
+		throw std::runtime_error(msg);
+	}
 	initExtensions();
 
 	static const GLenum BGRA8_EXT = 0x93A1;