diff --git a/models/scheduled_ticket.php b/models/scheduled_ticket.php
index 896148d5..38f05486 100644
--- a/models/scheduled_ticket.php
+++ b/models/scheduled_ticket.php
@@ -1,6 +1,6 @@
 <?php
 // HTML Purifier
-require("plugins/htmlpurifier/HTMLPurifier.standalone.php");
+require_once("plugins/htmlpurifier/HTMLPurifier.standalone.php");
 $purifier_config = HTMLPurifier_Config::createDefault();
 $purifier_config->set('URI.AllowedSchemes', ['data' => true, 'src' => true, 'http' => true, 'https' => true]);
 $purifier = new HTMLPurifier($purifier_config);