diff --git a/core/modules/config/tests/config_test/lib/Drupal/config_test/Entity/ConfigTest.php b/core/modules/config/tests/config_test/lib/Drupal/config_test/Entity/ConfigTest.php
index 07ec50a..6dbff85 100644
--- a/core/modules/config/tests/config_test/lib/Drupal/config_test/Entity/ConfigTest.php
+++ b/core/modules/config/tests/config_test/lib/Drupal/config_test/Entity/ConfigTest.php
@@ -48,7 +48,7 @@ class ConfigTest extends ConfigEntityBase implements ConfigTestInterface {
    *
    * @var string
    */
-  public $id;
+  protected $id;
 
   /**
    * The human-readable name of the configuration entity.