diff --git a/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
index e6c457b..6453832 100644
--- a/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
+++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
@@ -66,16 +66,17 @@ public function dispatch($event_name, Event $event = NULL) {
       // Sort listeners if necessary.
       if (!isset($this->sorted[$event_name])) {
         krsort($this->listeners[$event_name]);
+        $this->sorted[$event_name] = TRUE;
       }
 
       // Invoke listeners and resolve callables if necessary.
-      foreach ($this->listeners[$event_name] as $priority => $definitions) {
-        foreach ($definitions as $key => $definition) {
+      foreach ($this->listeners[$event_name] as $priority => &$definitions) {
+        foreach ($definitions as $key => &$definition) {
           if (!isset($definition['callable'])) {
             $definition['callable'] = [$this->container->get($definition['service'][0]), $definition['service'][1]];
           }
 
-          call_user_func($definition['callable'], $event, $event_name, $this);
+          $definition['callable']($event, $event_name, $this);
           if ($event->isPropagationStopped()) {
             return $event;
           }
@@ -105,11 +106,12 @@ public function getListeners($event_name = NULL) {
       // Sort listeners if necessary.
       if (!isset($this->sorted[$event_name])) {
         krsort($this->listeners[$event_name]);
+        $this->sorted[$event_name] = TRUE;
       }
 
       // Collect listeners and resolve callables if necessary.
-      foreach ($this->listeners[$event_name] as $priority => $definitions) {
-        foreach ($definitions as $key => $definition) {
+      foreach ($this->listeners[$event_name] as $priority => &$definitions) {
+        foreach ($definitions as $key => &$definition) {
           if (!isset($definition['callable'])) {
             $definition['callable'] = [$this->container->get($definition['service'][0]), $definition['service'][1]];
           }