diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index dc648e7e..360d723a 100644
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -166,7 +166,8 @@ static char *fmt_u(uintmax_t x, char *s)
 {
 	unsigned long y;
 	for (   ; x>ULONG_MAX; x/=10) *--s = '0' + x%10;
-	for (y=x;           y; y/=10) *--s = '0' + y%10;
+	for (y=x;       y>=10; y/=10) *--s = '0' + y%10;
+	if (y) *--s = '0' + y;
 	return s;
 }