diff -u b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php
--- b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntitySerializationTest.php
@@ -148,7 +148,34 @@
     $field_name = $this->entityReferenceFieldName;
     $user = $this->createUser();
 
-    // Case 1: new_entity->existing_entity->parent_new_entity
+    // Case 1: new_entity_a->new_entity_b->new_entity_a
+    /** @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_one = $entity_level_zero->createDuplicate();
+    $entity_level_one->setName('entity one');
+
+    // 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);
+    $this->assertEquals(1, substr_count($serialized_main_entity, 'entity zero'));
+    $this->assertEquals(1, substr_count($serialized_main_entity, 'entity one'));
+
+
+    // Case 2: existing_entity_a->existing_entity_b->existing_entity_a_cloned
     /** @var \Drupal\entity_test\Entity\EntityTestMul $entity_level_zero */
     $entity_level_zero = $this->entityStorage->create([
       'name' => 'entity zero',
@@ -160,7 +187,6 @@
     $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.
@@ -182,7 +208,7 @@
     $this->assertEquals(1, substr_count($serialized_main_entity, 'entity one'));
 
 
-    // Case 2:
+    // Case 3: existing_entity_a->existing_entity_b->existing_entity_a
     // 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());
@@ -202,6 +228,57 @@
     $serialized_main_entity = serialize($entity_level_zero);
     $this->assertEquals(2, substr_count($serialized_main_entity, 'entity zero'));
     $this->assertEquals(2, substr_count($serialized_main_entity, 'entity one'));
+
+
+    // Case 4 : Like the previous case, but now show that no matter how deep a
+    // nested structure with circular references is initialized the serialized
+    // string will remain the same and will contain the serialized values to the
+    // same amount as when the structure is not initialized that deep.
+
+    // 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);
+    $serialized_main_entity_case_4a = serialize($entity_level_zero);
+    $this->assertEquals(2, substr_count($serialized_main_entity_case_4a, 'entity zero'));
+    $this->assertEquals(2, substr_count($serialized_main_entity_case_4a, 'entity one'));
+
+    // 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->$field_name->entity->$field_name->entity->$field_name->entity;
+
+    // Now serialize the entity structure through deep serialization.
+    $entity_level_zero->setDeepSerialization(TRUE);
+    $serialized_main_entity_case_4b = serialize($entity_level_zero);
+    $this->assertEquals(2, substr_count($serialized_main_entity_case_4b, 'entity zero'));
+    $this->assertEquals(2, substr_count($serialized_main_entity_case_4b, 'entity one'));
+
+    // 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->$field_name->entity->$field_name->entity->$field_name->entity->$field_name->entity->$field_name->entity;
+
+    // Now serialize the entity structure through deep serialization.
+    $entity_level_zero->setDeepSerialization(TRUE);
+    $serialized_main_entity_case_4c = serialize($entity_level_zero);
+    $this->assertEquals(2, substr_count($serialized_main_entity_case_4c, 'entity zero'));
+    $this->assertEquals(2, substr_count($serialized_main_entity_case_4c, 'entity one'));
+
+    // Assert that the serialization result does not depend on how deep the
+    // nested structure with circular references is initialized.
+    $this->assertEquals($serialized_main_entity_case_4a, $serialized_main_entity_case_4b);
+    $this->assertEquals($serialized_main_entity_case_4b, $serialized_main_entity_case_4c);
   }
 
 }