diff --git a/ripngd/ripng_main.c b/ripngd/ripng_main.c
index 7055391..a18ce9d 100644
--- a/ripngd/ripng_main.c
+++ b/ripngd/ripng_main.c
@@ -240,7 +240,8 @@
               break;
             } 
           vty_port = atoi (optarg);
-          vty_port = (vty_port ? vty_port : RIPNG_VTY_PORT);
+          if (vty_port <= 0 || vty_port > 0xffff)
+            vty_port = RIPNG_VTY_PORT;
           break;
 	case 'r':
 	  retain_mode = 1;