diff --git a/protocol/handshake_open.go b/protocol/handshake_open.go
index 077f299..c6ac073 100644
--- a/protocol/handshake_open.go
+++ b/protocol/handshake_open.go
@@ -56,11 +56,12 @@ func (h HandshakeOpen) EncodeMsgpack(enc *msgpack.Encoder) error {
 		return err
 	}
 
-	err = enc.EncodeString(h.networkId)
-	if err != nil {
-		return err
+	if h.networkId != "" {
+		err = enc.EncodeString(h.networkId)
+		if err != nil {
+			return err
+		}
 	}
-
 	return nil
 }