diff --git a/upstream.go b/upstream.go
index a0f5d69..4d93221 100644
--- a/upstream.go
+++ b/upstream.go
@@ -1335,6 +1335,11 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 		// Ignore
 	case irc.RPL_STATSVLINE, rpl_statsping, irc.RPL_STATSBLINE, irc.RPL_STATSDLINE:
 		// Ignore
+	case irc.ERR_PASSWDMISMATCH, irc.ERR_ERRONEUSNICKNAME, irc.ERR_NICKNAMEINUSE, irc.ERR_NICKCOLLISION, irc.ERR_UNAVAILRESOURCE:
+		if !uc.registered {
+			return fmt.Errorf("registration failed: %v", msg.Params[len(msg.Params) - 1])
+		}
+		fallthrough
 	default:
 		uc.logger.Printf("unhandled message: %v", msg)
 		if downstreamID != 0 {