diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index c796baf4..af45ee78 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -1784,7 +1784,7 @@ class Net_SFTP extends Net_SSH2
      * @param optional Integer $mode
      * @param optional Integer $start
      * @param optional Integer $local_start
-     * @param optional Callable $callback
+     * @param optional callable|null $callback
      * @return Boolean
      * @access public
      * @internal ASCII mode for SFTPv4/5/6 can be supported by adding a new function - Net_SFTP::setMode().