diff -u b/core/modules/page_cache/src/EventSubscriber/ConfigSubscriber.php b/core/modules/page_cache/src/EventSubscriber/ConfigSubscriber.php
--- b/core/modules/page_cache/src/EventSubscriber/ConfigSubscriber.php
+++ b/core/modules/page_cache/src/EventSubscriber/ConfigSubscriber.php
@@ -29,7 +29,7 @@
   /**
    * {@inheritdoc}
    */
-  static function getSubscribedEvents() {
+  static public function getSubscribedEvents() {
     $events[ConfigEvents::SAVE][] = ['onConfigSave', 0];
     return $events;
   }