diff --git a/ftp.go b/ftp.go
index 648c90e..b0f6979 100644
--- a/ftp.go
+++ b/ftp.go
@@ -130,7 +130,7 @@ func (c *ServerConn) cmdDataConn(format string, args ...interface{}) (net.Conn,
 	}
 	if code != StatusAlreadyOpen && code != StatusAboutToSend {
 		conn.Close()
-		return nil, os.NewError(fmt.Sprintf("%d %s", code, msg))
+		return nil, &textproto.Error{code, msg}
 	}
 
 	return conn, nil