diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index ff48437..6c2a700 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -366,6 +366,7 @@ public function preSave(EntityStorageInterface $storage) {
    * {@inheritdoc}
    */
   public function __sleep() {
+    $keys_to_unset = [];
     if ($this instanceof EntityWithPluginCollectionInterface) {
       $vars = get_object_vars($this);
       // Any changes to the plugin configuration must be saved to the entity's
@@ -374,12 +375,16 @@ public function __sleep() {
         $this->set($plugin_config_key, $plugin_collection->getConfiguration());
         foreach ($vars as $key => $value) {
           if ($plugin_collection === $value) {
-            unset($vars[$key]);
+            $keys_to_unset[] = $key;
           }
         }
       }
     }
-    return parent::__sleep();
+    $vars = parent::__sleep();
+    foreach ($keys_to_unset as $key) {
+      unset($vars[array_search($key, $vars)]);
+    }
+    return $vars;
   }
 
   /**