diff --git a/cache/classes/form/cachestore_addinstance_form.php b/cache/classes/form/cachestore_addinstance_form.php
index 742c37f50bb..00f32a3d4ef 100644
--- a/cache/classes/form/cachestore_addinstance_form.php
+++ b/cache/classes/form/cachestore_addinstance_form.php
@@ -16,6 +16,11 @@
 
 namespace core_cache\form;
 
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->dirroot . '/lib/formslib.php');
+
 use core_cache\administration_helper;
 use moodleform;