diff --git a/src/vnet/udp/builtin_server.c b/src/vnet/udp/builtin_server.c
index 7dd0367..23f0854 100644
--- a/src/vnet/udp/builtin_server.c
+++ b/src/vnet/udp/builtin_server.c
@@ -115,7 +115,9 @@
 
   a->options = options;
 
-  return vnet_application_attach (a);
+  if (vnet_application_attach (a))
+    return -1;
+  return 0;
 }
 
 static int