diff --git a/mongoose.c b/mongoose.c
index 859c30ff..8f95fbca 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -9357,10 +9357,14 @@ static void mg_resolve_async_eh(struct mg_connection *nc, int ev, void *data) {
   struct mg_resolve_async_request *req;
   struct mg_dns_message *msg;
 
-  DBG(("ev=%d", ev));
+  DBG(("ev=%d user_data=%p", ev, nc->user_data));
 
   req = (struct mg_resolve_async_request *) nc->user_data;
 
+  if (req == NULL) {
+    return;
+  }
+
   switch (ev) {
     case MG_EV_CONNECT:
     case MG_EV_POLL: