diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index cf12ba86205c096eea6543e3c2850e384ca139c1..602d2081e713c802406e35888b996f6aea05823a 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -114,8 +114,9 @@ int skip_atoi(const char **s)
 {
 	int i = 0;
 
-	while (isdigit(**s))
+	do {
 		i = i*10 + *((*s)++) - '0';
+	} while (isdigit(**s));
 
 	return i;
 }