diff --git a/url.c b/url.c
index 25576c390b..1b8ef78cea 100644
--- a/url.c
+++ b/url.c
@@ -46,9 +46,9 @@ static char *url_decode_internal(const char **query, int len,
 			break;
 		}
 
-		if (c == '%') {
+		if (c == '%' && (len < 0 || len >= 3)) {
 			int val = hex2chr(q + 1);
-			if (0 <= val) {
+			if (0 < val) {
 				strbuf_addch(out, val);
 				q += 3;
 				len -= 3;