diff --git a/programs/winevdm/winevdm.c b/programs/winevdm/winevdm.c
index 5b5f72db253..87c25f0d191 100644
--- a/programs/winevdm/winevdm.c
+++ b/programs/winevdm/winevdm.c
@@ -359,7 +359,7 @@ static char *build_command_line( char **argv )
         return NULL;
 
     p = cmd_line;
-    *p++ = (len < 256) ? len : 255;
+    *p++ = (len < 256) ? len : '\xff';
     for (arg = argv; *arg; arg++)
     {
         BOOL has_space,has_quote;