--- usb_modeswitch_dispatcher.c.orig	2014-02-20 15:08:44.665397121 +0700
+++ usb_modeswitch_dispatcher.c	2014-02-20 17:04:27.269572144 +0700
@@ -838,7 +838,7 @@
 {
     char* back = s + strlen(s);
 
-    while(isspace(*--back));
+    while(back>=s && isspace(*--back));
 
     *(back+1) = '\0';