diff --git a/src/lib_aux.c b/src/lib_aux.c
index 5f4e3e8c..419650a9 100644
--- a/src/lib_aux.c
+++ b/src/lib_aux.c
@@ -313,6 +313,10 @@ LUALIB_API int luaL_loadstring(lua_State *L, const char *s)
 
 #ifdef LUAJIT_USE_SYSMALLOC
 
+#if LJ_64
+#error "Must use builtin allocator for 64 bit target"
+#endif
+
 static void *mem_alloc(void *ud, void *ptr, size_t osize, size_t nsize)
 {
   (void)ud;
diff --git a/src/lj_def.h b/src/lj_def.h
index 8128aa21..872a7830 100644
--- a/src/lj_def.h
+++ b/src/lj_def.h
@@ -89,6 +89,7 @@ typedef unsigned __int32 uintptr_t;
 #define checku8(x)	((x) == (int32_t)(uint8_t)(x))
 #define checki16(x)	((x) == (int32_t)(int16_t)(x))
 #define checku16(x)	((x) == (int32_t)(uint16_t)(x))
+#define checkptr32(x)	((uintptr_t)(x) == (uint32_t)(uintptr_t)(x))
 
 /* Every half-decent C compiler transforms this into a rotate instruction. */
 #define lj_rol(x, n)	(((x)<<(n)) | ((x)>>(32-(n))))
diff --git a/src/lj_gc.c b/src/lj_gc.c
index cd99f249..764d74a8 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -764,6 +764,7 @@ void *lj_mem_realloc(lua_State *L, void *p, MSize osz, MSize nsz)
   if (p == NULL && nsz > 0)
     lj_err_throw(L, LUA_ERRMEM);
   lua_assert((nsz == 0) == (p == NULL));
+  lua_assert(checkptr32(p));
   g->gc.total = (g->gc.total - osz) + nsz;
   return p;
 }
@@ -775,6 +776,7 @@ void *lj_mem_newgco(lua_State *L, MSize size)
   GCobj *o = (GCobj *)g->allocf(g->allocd, NULL, 0, size);
   if (o == NULL)
     lj_err_throw(L, LUA_ERRMEM);
+  lua_assert(checkptr32(o));
   g->gc.total += size;
   setgcrefr(o->gch.nextgc, g->gc.root);
   setgcref(g->gc.root, o);
diff --git a/src/lj_state.c b/src/lj_state.c
index e1b9021e..f7f30117 100644
--- a/src/lj_state.c
+++ b/src/lj_state.c
@@ -163,7 +163,7 @@ LUA_API lua_State *lua_newstate(lua_Alloc f, void *ud)
   GG_State *GG = cast(GG_State *, f(ud, NULL, 0, sizeof(GG_State)));
   lua_State *L = &GG->L;
   global_State *g = &GG->g;
-  if (GG == NULL) return NULL;
+  if (GG == NULL || !checkptr32(GG)) return NULL;
   memset(GG, 0, sizeof(GG_State));
   L->gct = ~LJ_TTHREAD;
   L->marked = LJ_GC_WHITE0 | LJ_GC_FIXED | LJ_GC_SFIXED;  /* Prevent free. */