diff --git a/classes/event/otp_generated.php b/classes/event/otp_generated.php
index 6ac2d08..d3d87ff 100644
--- a/classes/event/otp_generated.php
+++ b/classes/event/otp_generated.php
@@ -35,13 +35,13 @@ defined('MOODLE_INTERNAL') || die();
  */
 class otp_generated extends \core\event\base {
 
-    protected static $crud = 'c';
+    protected const CRUD = 'c';
 
     /**
      * {@inheritdoc}
      */
     protected function init() {
-        $this->data['crud'] = static::$crud; 
+        $this->data['crud'] = static::CRUD;
         $this->data['edulevel'] = self::LEVEL_OTHER;
         $this->context = \context_system::instance();
     }
diff --git a/classes/event/otp_revoked.php b/classes/event/otp_revoked.php
index 14001a6..d9c4c29 100644
--- a/classes/event/otp_revoked.php
+++ b/classes/event/otp_revoked.php
@@ -34,5 +34,5 @@ defined('MOODLE_INTERNAL') || die();
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class otp_revoked extends otp_generated {
-    protected static $crud = 'd';
+    protected const CRUD = 'd';
 }