diff --git a/lgc.h b/lgc.h
index a5baebcb..aa76ab11 100644
--- a/lgc.h
+++ b/lgc.h
@@ -16,7 +16,7 @@
 
 
 void luaC_callallgcTM (lua_State *L);
-Udata *luaC_collect (lua_State *L, int all);
+void luaC_collect (lua_State *L, int all);
 void luaC_collectgarbage (lua_State *L);
 
 
diff --git a/lstate.c b/lstate.c
index 7777b7a1..35518cbc 100644
--- a/lstate.c
+++ b/lstate.c
@@ -116,7 +116,8 @@ static void close_state (lua_State *L, lua_State *OL) {
     L->next->previous = L->previous;
   }
   else if (G(L)) {  /* last thread; close global state */
-    luaC_callallgcTM(L);  /* call GC tag methods for all udata */
+    if (G(L)->rootudata)  /* (avoid problems with incomplete states) */
+      luaC_callallgcTM(L);  /* call GC tag methods for all udata */
     luaC_collect(L, 1);  /* collect all elements */
     lua_assert(G(L)->rootproto == NULL);
     lua_assert(G(L)->rootudata == NULL);