diff -u b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
--- b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
@@ -28,7 +28,7 @@
    * @param string $id
    *   The new ID to set as original ID.
    *
-   * @return \Drupal\Core\Config\Entity\ConfigEntityInterface
+   * @return self
    */
   public function setOriginalId($id);
 
diff -u b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityUnitTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityUnitTest.php
--- b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityUnitTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityUnitTest.php
@@ -92,7 +92,7 @@
   protected function testGetOriginalId() {
     $entity = $this->storage->create(array());
     $id = $this->randomName();
-    $this->assertTrue($entity->setOriginalId($id) instanceof EntityInterface);
+    $this->assertIdentical(spl_object_hash($entity->setOriginalId($id)), spl_object_hash($entity));
     $this->assertIdentical($entity->getOriginalId(), $id);
   }