diff --git a/downstream.go b/downstream.go
index 153c3f9..c4d39f6 100644
--- a/downstream.go
+++ b/downstream.go
@@ -1290,7 +1290,7 @@ func (dc *downstreamConn) register(ctx context.Context) error {
 	_, fallbackClientName, fallbackNetworkName := unmarshalUsername(dc.rawUsername)
 	if dc.clientName == "" {
 		dc.clientName = fallbackClientName
-	} else if dc.clientName != fallbackClientName {
+	} else if fallbackClientName != "" && dc.clientName != fallbackClientName {
 		return ircError{&irc.Message{
 			Command: irc.ERR_ERRONEUSNICKNAME,
 			Params:  []string{dc.nick, "Client name mismatch in usernames"},
@@ -1298,7 +1298,7 @@ func (dc *downstreamConn) register(ctx context.Context) error {
 	}
 	if dc.networkName == "" {
 		dc.networkName = fallbackNetworkName
-	} else if dc.networkName != fallbackNetworkName {
+	} else if fallbackNetworkName != "" && dc.networkName != fallbackNetworkName {
 		return ircError{&irc.Message{
 			Command: irc.ERR_ERRONEUSNICKNAME,
 			Params:  []string{dc.nick, "Network name mismatch in usernames"},