diff --git a/src/gui/lua/lua_threads.cpp b/src/gui/lua/lua_threads.cpp
index c4f7fdee3..6a63c8bd5 100644
--- a/src/gui/lua/lua_threads.cpp
+++ b/src/gui/lua/lua_threads.cpp
@@ -174,7 +174,7 @@ llthread_t *CLLThread::llthread_create(lua_State *L, const char *code, size_t co
 			/* non-string error message. */
 			lua_pushfstring(L, "luaL_loadbuffer() failed to load Lua code: rc=%d", rc);
 		}
-		/*    llthread_destroy(_this); */
+		llthread_destroy(_this);
 		lua_error(L);
 		return NULL;
 	}
diff --git a/src/gui/lua/lua_threads_functions.cpp b/src/gui/lua/lua_threads_functions.cpp
index 3d8f210cc..ac8df53fb 100644
--- a/src/gui/lua/lua_threads_functions.cpp
+++ b/src/gui/lua/lua_threads_functions.cpp
@@ -263,7 +263,7 @@ int CLLThread::l_llthread_delete(lua_State *L)
 {
 	llthread_t **pthis = (llthread_t **)luaL_checkudata(L, 1, LLTHREAD_TAG);
 	luaL_argcheck (L, pthis != NULL, 1, "thread expected");
-	if (*pthis == NULL) return 0;
+	if (pthis == NULL || *pthis == NULL) return 0;
 	llthread_destroy(*pthis);
 	*pthis = NULL;
 
diff --git a/src/gui/lua/luainstance.cpp b/src/gui/lua/luainstance.cpp
index 3a7f44ab3..6c7516e4a 100644
--- a/src/gui/lua/luainstance.cpp
+++ b/src/gui/lua/luainstance.cpp
@@ -625,8 +625,10 @@ CLuaData *CLuaInstance::CheckData(lua_State *L, int narg)
 {
 	luaL_checktype(L, narg, LUA_TUSERDATA);
 	void *ud = luaL_checkudata(L, narg, className);
-	if (!ud)
+	if (!ud) {
 		fprintf(stderr, "[CLuaInstance::%s] wrong type %p, %d, %s\n", __func__, L, narg, className);
+		return NULL;
+	}
 	return *(CLuaData **)ud;  // unbox pointer
 }