diff --git a/zebra/test_main.c b/zebra/test_main.c
index 4398a38..70a1a3a 100644
--- a/zebra/test_main.c
+++ b/zebra/test_main.c
@@ -270,7 +270,11 @@
   
   /* port and conf file mandatory */
   if (!vty_port || !config_file)
-    usage (progname, 1);
+    {
+      fprintf (stderr, "Error: --vty_port and --config_file arguments"
+                       " are both required\n");
+      usage (progname, 1);
+    }
   
   /* Make master thread emulator. */
   zebrad.master = thread_master_create ();