mse/cmd/mse/main.go | 5 ++++-

diff --git a/mse/cmd/mse/main.go b/mse/cmd/mse/main.go
index c4311ca379eea809e3e5a646ddb0caabaa53d8b5..2d90398a085bc7b72ac8b4f0331e49b1feeae1e6 100644
--- a/mse/cmd/mse/main.go
+++ b/mse/cmd/mse/main.go
@@ -37,7 +37,7 @@ 		} `arg:"subcommand""`
 	}{
 		CryptoMethod: mse.AllSupportedCrypto,
 	}
-	arg.MustParse(&args)
+	p := arg.MustParse(&args)
 	if args.Dial != nil {
 		cn, err := net.Dial(args.Dial.Network, args.Dial.Address)
 		if err != nil {
@@ -71,6 +71,9 @@ 		if err != nil {
 			log.Fatalf("error receiving: %v", err)
 		}
 		doStreaming(rw)
+	}
+	if p.Subcommand() == nil {
+		p.Fail("missing subcommand")
 	}
 	return nil
 }