diff --git a/src/webclient.c b/src/webclient.c
index 83ae8aa..7182418 100644
--- a/src/webclient.c
+++ b/src/webclient.c
@@ -178,6 +178,8 @@ static int webclient_resolve_address(struct webclient_session *session, struct a
     RT_ASSERT(res);
     RT_ASSERT(request);
 
+    /* make sure *res = NULL before getaddrinfo */
+    *res = RT_NULL;
     url_len = rt_strlen(url);
 
     /* strip protocol(http or https) */