diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
index a9b6d97..d23341b 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
@@ -220,9 +220,9 @@ public function save(EntityInterface $entity) {
     // @see \Drupal\Core\Config\Entity\ConfigEntityStorage::MAX_ID_LENGTH
     // @todo Consider moving this to a protected method on the parent class, and
     //   abstracting it for all entity types.
-    if (strlen($entity->{$this->idKey}) > self::MAX_ID_LENGTH) {
+    if (strlen($entity->get($this->idKey)) > self::MAX_ID_LENGTH) {
       throw new ConfigEntityIdLengthException(String::format('Configuration entity ID @id exceeds maximum allowed length of @length characters.', array(
-        '@id' => $entity->{$this->idKey},
+        '@id' => $entity->get($this->idKey),
         '@length' => self::MAX_ID_LENGTH,
       )));
     }
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.