diff --git a/include/NotificationsManager.php b/include/NotificationsManager.php
index c99d00742c..5f8211eb87 100644
--- a/include/NotificationsManager.php
+++ b/include/NotificationsManager.php
@@ -2,6 +2,7 @@
 /**
  * @file include/NotificationsManager.php
  */
+require_once('include/html2plain.php');
 require_once("include/datetime.php");
 require_once("include/bbcode.php");