diff --git a/lib/outputcomponents.php b/lib/outputcomponents.php
index 3ec3b99642f..a1be437ba48 100644
--- a/lib/outputcomponents.php
+++ b/lib/outputcomponents.php
@@ -4747,6 +4747,10 @@ class progress_bar implements renderable, templatable {
      * @param bool $autostart Whether to start the progress bar right away.
      */
     public function __construct($htmlid = '', $width = 500, $autostart = false) {
+        if (!defined('NO_OUTPUT_BUFFERING') || !NO_OUTPUT_BUFFERING) {
+            debugging('progress_bar used without setting NO_OUTPUT_BUFFERING.', DEBUG_DEVELOPER);
+        }
+
         if (!empty($htmlid)) {
             $this->html_id  = $htmlid;
         } else {