diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 1d659d7..c112056 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -898,7 +898,7 @@
 	case 'U':
 		return uuid_string(buf, end, ptr, spec, fmt);
 	case 'V':
-		return buf + vsnprintf(buf, end - buf,
+		return buf + vsnprintf(buf, end > buf ? end - buf : 0,
 				       ((struct va_format *)ptr)->fmt,
 				       *(((struct va_format *)ptr)->va));
 	case 'K':