diff --git a/lib/lua/README.md b/lib/lua/README.md
new file mode 100644
index 000000000..b82e4a652
--- /dev/null
+++ b/lib/lua/README.md
@@ -0,0 +1,6 @@
+## Lua 5.1.5 source
+
+This copy has been patched with Minetest-specific changes (`lua_atccall`)
+so it is *not* interchangeable with upstream PUC Lua.
+
+A patch for CVE-2014-5461 has been applied.
diff --git a/lib/lua/src/lbaselib.c b/lib/lua/src/lbaselib.c
index 2ab550bd4..ed293ebdc 100644
--- a/lib/lua/src/lbaselib.c
+++ b/lib/lua/src/lbaselib.c
@@ -340,13 +340,14 @@ static int luaB_assert (lua_State *L) {
 
 
 static int luaB_unpack (lua_State *L) {
-  int i, e, n;
+  int i, e;
+  unsigned int n;
   luaL_checktype(L, 1, LUA_TTABLE);
   i = luaL_optint(L, 2, 1);
   e = luaL_opt(L, luaL_checkint, 3, luaL_getn(L, 1));
   if (i > e) return 0;  /* empty range */
-  n = e - i + 1;  /* number of elements */
-  if (n <= 0 || !lua_checkstack(L, n))  /* n <= 0 means arith. overflow */
+  n = (unsigned int)e - (unsigned int)i;  /* number of elements minus 1 */
+  if (n > (INT_MAX - 10) || !lua_checkstack(L, ++n))
     return luaL_error(L, "too many results to unpack");
   lua_rawgeti(L, 1, i);  /* push arg[i] (avoiding overflow problems) */
   while (i++ < e)  /* push arg[i + 1...e] */
diff --git a/lib/lua/src/ldblib.c b/lib/lua/src/ldblib.c
index 628a6c458..2c55edcda 100644
--- a/lib/lua/src/ldblib.c
+++ b/lib/lua/src/ldblib.c
@@ -101,6 +101,7 @@ static int db_getinfo (lua_State *L) {
   int arg;
   lua_State *L1 = getthread(L, &arg);
   const char *options = luaL_optstring(L, arg+2, "flnSu");
+  luaL_argcheck(L, options[0] != '>', arg + 2, "invalid option '>'");
   if (lua_isnumber(L, arg+1)) {
     if (!lua_getstack(L1, (int)lua_tointeger(L, arg+1), &ar)) {
       lua_pushnil(L);  /* level out of range */
diff --git a/lib/lua/src/ldo.c b/lib/lua/src/ldo.c
index 7eeea636c..37a7660fd 100644
--- a/lib/lua/src/ldo.c
+++ b/lib/lua/src/ldo.c
@@ -274,7 +274,7 @@ int luaD_precall (lua_State *L, StkId func, int nresults) {
     CallInfo *ci;
     StkId st, base;
     Proto *p = cl->p;
-    luaD_checkstack(L, p->maxstacksize);
+    luaD_checkstack(L, p->maxstacksize + p->numparams);
     func = restorestack(L, funcr);
     if (!p->is_vararg) {  /* no varargs? */
       base = func + 1;
diff --git a/lib/lua/src/llex.c b/lib/lua/src/llex.c
index d1b179670..5affe7c16 100644
--- a/lib/lua/src/llex.c
+++ b/lib/lua/src/llex.c
@@ -133,7 +133,7 @@ static void inclinenumber (LexState *ls) {
   if (currIsNewline(ls) && ls->current != old)
     next(ls);  /* skip `\n\r' or `\r\n' */
   if (++ls->linenumber >= MAX_INT)
-    luaX_syntaxerror(ls, "chunk has too many lines");
+    luaX_lexerror(ls, "chunk has too many lines", 0);
 }
 
 
diff --git a/lib/lua/src/lvm.c b/lib/lua/src/lvm.c
index a438d7805..60a715a6d 100644
--- a/lib/lua/src/lvm.c
+++ b/lib/lua/src/lvm.c
@@ -209,14 +209,15 @@ static int l_strcmp (const TString *ls, const TString *rs) {
     int temp = strcoll(l, r);
     if (temp != 0) return temp;
     else {  /* strings are equal up to a `\0' */
-      size_t len = strlen(l);  /* index of first `\0' in both strings */
-      if (len == lr)  /* r is finished? */
-        return (len == ll) ? 0 : 1;
-      else if (len == ll)  /* l is finished? */
-        return -1;  /* l is smaller than r (because r is not finished) */
-      /* both strings longer than `len'; go on comparing (after the `\0') */
-      len++;
-      l += len; ll -= len; r += len; lr -= len;
+      size_t zl1 = strlen(l);  /* index of first '\0' in 'l' */
+      size_t zl2 = strlen(r);  /* index of first '\0' in 'r' */
+      if (zl2 == lr)  /* 'r' is finished? */
+        return (zl1 == ll) ? 0 : 1;  /* check 'l' */
+      else if (zl1 == ll)  /* 'l' is finished? */
+        return -1;  /* 'l' is less than 'r' ('r' is not finished) */
+      /* both strings longer than 'zl'; go on comparing after the '\0' */
+      zl1++; zl2++;
+      l += zl1; ll -= zl1; r += zl2; lr -= zl2;
     }
   }
 }