diff -rub john-1.7.8/src/MSCHAPv2_fmt_plug.c john-1.7.8-jmk/src/MSCHAPv2_fmt_plug.c
--- john-1.7.8/src/MSCHAPv2_fmt_plug.c	2011-09-26 16:13:11.432105174 -0500
+++ john-1.7.8-jmk/src/MSCHAPv2_fmt_plug.c	2011-09-26 16:13:59.312105174 -0500
@@ -145,7 +145,7 @@
   /* Validate Username Length */
   pos2++; pos = pos2;
   for (; atoi16[ARCH_INDEX(*pos2)] != 0x7F; pos2++);
-  if ( !(*pos2 && (pos2 - pos <= USERNAME_LENGTH)) )
+  if (pos2 - pos > USERNAME_LENGTH)
     return 0;
 
   return 1;