diff --git a/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
index caead14..76016b7 100644
--- a/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
+++ b/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php
@@ -62,11 +62,11 @@ class ContainerAwareEventDispatcher implements EventDispatcherInterface {
   protected $listeners;
 
   /**
-   * Whether event listeners are ordered, keyed by event name.
+   * Whether listeners need to be sorted prior to dispatch, keyed by event name.
    *
    * @var TRUE[]
    */
-  protected $sorted;
+  protected $unsorted;
 
   /**
    * Constructs a container aware event dispatcher.
@@ -85,7 +85,7 @@ class ContainerAwareEventDispatcher implements EventDispatcherInterface {
   public function __construct(IntrospectableContainerInterface $container, array $listeners = []) {
     $this->container = $container;
     $this->listeners = $listeners;
-    $this->sorted = array_fill_keys(array_keys($this->listeners), TRUE);
+    $this->unsorted = [];
   }
 
   /**
@@ -101,9 +101,9 @@ public function dispatch($event_name, Event $event = NULL) {
 
     if (isset($this->listeners[$event_name])) {
       // Sort listeners if necessary.
-      if (!isset($this->sorted[$event_name])) {
+      if (isset($this->unsorted[$event_name])) {
         krsort($this->listeners[$event_name]);
-        $this->sorted[$event_name] = TRUE;
+        unset($this->unsorted[$event_name]);
       }
 
       // Invoke listeners and resolve callables if necessary.
@@ -141,9 +141,9 @@ public function getListeners($event_name = NULL) {
     }
     elseif (isset($this->listeners[$event_name])) {
       // Sort listeners if necessary.
-      if (!isset($this->sorted[$event_name])) {
+      if (isset($this->unsorted[$event_name])) {
         krsort($this->listeners[$event_name]);
-        $this->sorted[$event_name] = TRUE;
+        unset($this->unsorted[$event_name]);
       }
 
       // Collect listeners and resolve callables if necessary.
@@ -173,7 +173,7 @@ public function hasListeners($event_name = NULL) {
    */
   public function addListener($event_name, $listener, $priority = 0) {
     $this->listeners[$event_name][$priority][] = ['callable' => $listener];
-    unset($this->sorted[$event_name]);
+    $this->unsorted[$event_name] = TRUE;
   }
 
   /**