diff --git a/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php
index f40d4ed..07dad80 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php
@@ -141,4 +141,67 @@ protected function doTestSerialization($deep_serialization) {
     $this->assertEquals($deep_serialization ? 'test deep serialization on language property' : $original_language_name, $language->getName());
   }
 
+  /**
+   * Tests deep serialization with circular entity references.
+   */
+  public function testDeepSerializationWithCircularEntityReferences() {
+    $field_name = $this->entityReferenceFieldName;
+    $user = $this->createUser();
+
+    // Case 1: new_entity->existing_entity->parent_new_entity
+    /** @var \Drupal\entity_test\Entity\EntityTestMul $entity_level_zero */
+    $entity_level_zero = $this->entityStorage->create([
+      'name' => 'entity zero',
+      'user_id' => $user->id(),
+      'language' => 'en',
+    ]);
+    $entity_level_zero->save();
+    $entity_level_one = $entity_level_zero->createDuplicate();
+    $entity_level_one->setName('entity one');
+    $entity_level_one->save();
+
+    // Case 1:
+    // Create a circular reference, where the parent entity is referenced at the
+    // end of the chain back again with a different object reference than the
+    // one at the beginning of the chain.
+    $entity_level_zero->$field_name->appendItem($entity_level_one);
+    // Ensure that the main entity has different object references by cloning
+    // it, otherwise PHP will not serialize the same object twice.
+    $entity_level_zero_clone = clone $entity_level_zero;
+    $this->assertNotSame($entity_level_zero, $entity_level_zero_clone);
+    $entity_level_one->$field_name->appendItem($entity_level_zero_clone);
+
+    // Make sure all the entities are initialized in the structure, otherwise
+    // they will not be contained in the serialization.
+    $entity_level_zero->$field_name->entity->$field_name->entity;
+
+    // Now serialize the entity structure through deep serialization.
+    $entity_level_zero->setDeepSerialization(TRUE);
+    $serialized_main_entity = serialize($entity_level_zero);
+    $this->assertEquals(2, substr_count($serialized_main_entity, 'entity zero'));
+    $this->assertEquals(1, substr_count($serialized_main_entity, 'entity one'));
+
+
+    // Case 2:
+    // Reset the entities for the next test.
+    $entity_level_zero = $this->entityStorage->loadUnchanged($entity_level_zero->id());
+    $entity_level_one = $this->entityStorage->loadUnchanged($entity_level_one->id());
+
+    // Create a circular reference, where the parent entity is referenced at the
+    // end of the chain back again with the same object reference as at the
+    // beginning of the chain.
+    $entity_level_zero->$field_name->appendItem($entity_level_one);
+    $entity_level_one->$field_name->appendItem($entity_level_zero);
+
+    // Make sure all the entities are initialized in the structure, otherwise
+    // they will not be contained in the serialization.
+    $entity_level_zero->$field_name->entity->$field_name->entity;
+
+    // Now serialize the entity structure through deep serialization.
+    $entity_level_zero->setDeepSerialization(TRUE);
+    $serialized_main_entity = serialize($entity_level_zero);
+    $this->assertEquals(2, substr_count($serialized_main_entity, 'entity zero'));
+    $this->assertEquals(2, substr_count($serialized_main_entity, 'entity one'));
+  }
+
 }