diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index 9249421c..29f692a7 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -1516,7 +1516,7 @@ class Net_SFTP extends Net_SSH2 {
         $sftp_packet_size = 4096; // PuTTY uses 4096
         $i = 0;
         while ($sent < $size) {
-            $temp = $mode & NET_SFTP_LOCAL_FILE ? fread($fp, $sftp_packet_size) : $this->_string_shift($data, $sftp_packet_size);
+            $temp = $mode & NET_SFTP_LOCAL_FILE ? fread($fp, $sftp_packet_size) : substr($data, $sent, $sftp_packet_size);
             $subtemp = $offset + $sent;
             $packet = pack('Na*N3a*', strlen($handle), $handle, $subtemp / 0x100000000, $subtemp, strlen($temp), $temp);
             if (!$this->_send_sftp_packet(NET_SFTP_WRITE, $packet)) {
@@ -2201,4 +2201,4 @@ class Net_SFTP extends Net_SSH2 {
         $this->pwd = false;
         parent::_disconnect($reason);
     }
-}
\ No newline at end of file
+}