diff --git a/core/modules/options/lib/Drupal/options/Plugin/Field/FieldType/ListBooleanItem.php b/core/modules/options/lib/Drupal/options/Plugin/Field/FieldType/ListBooleanItem.php
index a521459..76de3b7 100644
--- a/core/modules/options/lib/Drupal/options/Plugin/Field/FieldType/ListBooleanItem.php
+++ b/core/modules/options/lib/Drupal/options/Plugin/Field/FieldType/ListBooleanItem.php
@@ -31,10 +31,10 @@ class ListBooleanItem extends FieldItemBase implements AllowedValuesInterface {
    * {@inheritdoc}
    */
   public static function defaultSettings() {
-    $settings = parent::defaultSettings();
-    $settings['allowed_values'] = array();
-    $settings['allowed_values_function'] = '';
-    return $settings;
+    return array(
+      'allowed_values' => array(),
+      'allowed_values_function' => '',
+    ) + parent::defaultSettings();
   }
 
   /**