diff --git a/lib/outputrenderers.php b/lib/outputrenderers.php
index bf6a3f4321455..1f3816781c2ac 100644
--- a/lib/outputrenderers.php
+++ b/lib/outputrenderers.php
@@ -2615,12 +2615,14 @@ public function fatal_error($message, $moreinfourl, $link, $backtrace, $debuginf
 
         if (debugging('', DEBUG_DEVELOPER)) {
             if (!empty($debuginfo)) {
-                $this->notification($debuginfo, 'notifytiny');
+                $output .= $this->notification($debuginfo, 'notifytiny');
             }
             if (!empty($backtrace)) {
-                $this->notification('Stack trace: ' . format_backtrace($backtrace, true), 'notifytiny');
+                $output .= $this->notification('Stack trace: ' . format_backtrace($backtrace, true), 'notifytiny');
             }
         }
+
+        return $output;
     }
 
     /**