diff --git a/src/lparser.cpp b/src/lparser.cpp
index 7515644aad..7ad1c7668e 100644
--- a/src/lparser.cpp
+++ b/src/lparser.cpp
@@ -1519,7 +1519,8 @@ static void applyextends (LexState *ls, expdesc *v, TString *parent, int line) {
 
   expdesc f;
   singlevaraux(fs, luaS_newliteral(ls->L, "Pluto_operator_extends"), &f, 1);
-  lua_assert(f.k != VVOID);
+  if (f.k == VVOID)
+    luaX_syntaxerror(ls, "what the fuck?");
   luaK_exp2nextreg(fs, &f);
 
   expdesc args = *v;