diff --git a/src/lua_hooklib.c b/src/lua_hooklib.c
index 287a185bc..d5f1cf25e 100644
--- a/src/lua_hooklib.c
+++ b/src/lua_hooklib.c
@@ -347,6 +347,10 @@ static boolean prepare_mobj_hook
 		int          hook_type,
 		mobjtype_t   mobj_type
 ){
+#ifdef PARANOIA
+	if (mobj_type == MT_NULL)
+		I_Error("MT_NULL has been passed to a mobj hook\n");
+#endif
 	return init_hook_type(hook, default_status,
 			hook_type, mobj_type, NULL,
 			mobj_hook_available(hook_type, mobj_type));