diff --git a/grade/edit/tree/index.php b/grade/edit/tree/index.php
index b898b99ea4d..aa58497756d 100644
--- a/grade/edit/tree/index.php
+++ b/grade/edit/tree/index.php
@@ -22,6 +22,8 @@
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+define('NO_OUTPUT_BUFFERING', true); // The progress bar may be used here.
+
 require_once '../../../config.php';
 require_once $CFG->dirroot.'/grade/lib.php';
 require_once $CFG->dirroot.'/grade/report/lib.php'; // for preferences