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/lib/Drupal/config/Tests/ConfigEntityTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
index f3ca94f..776c6ee 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
@@ -47,7 +47,6 @@ function testCRUD() {
     $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
     // Verify default properties on a newly created empty entity.
     $empty = entity_create('config_test');
-    $this->assertIdentical($empty->id, NULL);
     $this->assertTrue($empty->uuid);
     $this->assertIdentical($empty->label, NULL);
     $this->assertIdentical($empty->style, NULL);
@@ -106,7 +105,6 @@ function testCRUD() {
       'label' => $this->randomString(),
       'style' => $this->randomName(),
     ));
-    $this->assertIdentical($config_test->id, $expected['id']);
     $this->assertTrue($config_test->uuid);
     $this->assertNotEqual($config_test->uuid, $empty->uuid);
     $this->assertIdentical($config_test->label, $expected['label']);
@@ -160,7 +158,7 @@ function testCRUD() {
     try {
       $id_length_config_test->save();
       $this->pass(String::format("config_test entity with ID length @length was saved.", array(
-        '@length' => strlen($id_length_config_test->id))
+        '@length' => strlen($id_length_config_test->id()))
       ));
     }
     catch (ConfigEntityIdLengthException $e) {
@@ -174,7 +172,7 @@ function testCRUD() {
     try {
       $id_length_config_test->save();
       $this->pass(String::format("config_test entity with ID length @length was saved.", array(
-        '@length' => strlen($id_length_config_test->id),
+        '@length' => strlen($id_length_config_test->id()),
       )));
     }
     catch (ConfigEntityIdLengthException $e) {
@@ -188,13 +186,13 @@ function testCRUD() {
     try {
       $status = $id_length_config_test->save();
       $this->fail(String::format("config_test entity with ID length @length exceeding the maximum allowed length of @max saved successfully", array(
-        '@length' => strlen($id_length_config_test->id),
+        '@length' => strlen($id_length_config_test->id()),
         '@max' => static::MAX_ID_LENGTH,
       )));
     }
     catch (ConfigEntityIdLengthException $e) {
       $this->pass(String::format("config_test entity with ID length @length exceeding the maximum allowed length of @max failed to save", array(
-        '@length' => strlen($id_length_config_test->id),
+        '@length' => strlen($id_length_config_test->id()),
         '@max' => static::MAX_ID_LENGTH,
       )));
     }
@@ -222,7 +220,7 @@ function testCRUD() {
       $this->assertIdentical($config_test->getOriginalId(), $old_id);
 
       // Rename.
-      $config_test->id = $new_id;
+      $config_test->set('id', $new_id);
       $this->assertIdentical($config_test->id(), $new_id);
       $status = $config_test->save();
       $this->assertIdentical($status, SAVED_UPDATED);
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..b50dde0 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.
@@ -91,6 +91,7 @@ class ConfigTest extends ConfigEntityBase implements ConfigTestInterface {
   public function toArray() {
     $properties = parent::toArray();
     $protected_names = array(
+      'id',
       'protected_property',
     );
     foreach ($protected_names as $name) {