diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index cf12ba8..602d208 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -114,8 +114,9 @@
 {
 	int i = 0;
 
-	while (isdigit(**s))
+	do {
 		i = i*10 + *((*s)++) - '0';
+	} while (isdigit(**s));
 
 	return i;
 }