diff --git a/file.php b/file.php
index b8ba8fded49..0e18cb55eb4 100644
--- a/file.php
+++ b/file.php
@@ -129,6 +129,7 @@
     // ========================================
     // finally send the file
     // ========================================
+    session_write_close(); // unlock session during fileserving
     $filename = $args[count($args)-1];
     send_file($pathname, $filename, $lifetime, !empty($CFG->filteruploadedfiles));