--- lcformat.c	2010-08-06 22:38:51.515625000 +0200
+++ dll\win32\kernel32\misc\lcformat.c	2010-08-06 22:41:55.109375000 +0200
@@ -1047,8 +1047,10 @@
   TRACE("(0x%04x,0x%08x,%s,%p,%p,%d)\n", lcid, dwFlags, debugstr_w(lpszValue),
         lpFormat, lpNumberStr, cchOut);
 
+  lcid = ConvertDefaultLocale(lcid);
+
   if (!lpszValue || cchOut < 0 || (cchOut > 0 && !lpNumberStr) ||
-      !IsValidLocale(lcid, 0) ||
+      !IsValidLocale(lcid, LCID_INSTALLED) ||
       (lpFormat && (dwFlags || !lpFormat->lpDecimalSep || !lpFormat->lpThousandSep)))
   {
     goto error;