--- lua-5.1.4.orig/src/lstrlib.c	2008/07/11 17:27:21	1.132.1.4
+++ lua-5.1.4/src/lstrlib.c	2010/05/14 15:12:53
@@ -754,6 +754,7 @@
 
 
 static int str_format (lua_State *L) {
+  int top = lua_gettop(L);
   int arg = 1;
   size_t sfl;
   const char *strfrmt = luaL_checklstring(L, arg, &sfl);
@@ -768,7 +769,8 @@
     else { /* format item */
       char form[MAX_FORMAT];  /* to store the format (`%...') */
       char buff[MAX_ITEM];  /* to store the formatted item */
-      arg++;
+      if (++arg > top)
+        luaL_argerror(L, arg, "no value");
       strfrmt = scanformat(L, strfrmt, form);
       switch (*strfrmt++) {
         case 'c': {