diff --git a/core/lib/Drupal/Core/TypedData/TypedDataManager.php b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
index 9206d23..df26422 100644
--- a/core/lib/Drupal/Core/TypedData/TypedDataManager.php
+++ b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
@@ -255,7 +255,7 @@ public function getPropertyInstance(TypedDataInterface $object, $property_name,
     }
     $key = $definition->getDataType();
     if ($settings = $definition->getSettings()) {
-      $key .= ':' . implode(',', $settings);
+      $key .= ':' . serialize($settings);
     }
     $key .= ':' . $object->getPropertyPath() . '.';
     // If we are creating list items, we always use 0 in the key as all list
diff --git a/core/modules/system/src/Tests/Entity/EntityUnitTestBase.php b/core/modules/system/src/Tests/Entity/EntityUnitTestBase.php
index ada31f2..c1dc0ff 100644
--- a/core/modules/system/src/Tests/Entity/EntityUnitTestBase.php
+++ b/core/modules/system/src/Tests/Entity/EntityUnitTestBase.php
@@ -20,7 +20,7 @@
    *
    * @var array
    */
-  public static $modules = array('entity', 'user', 'system', 'field', 'text', 'filter', 'entity_test');
+  public static $modules = array('entity', 'user', 'system', 'field', 'text', 'filter', 'entity_test', 'entity_reference');
 
   /**
    * The entity manager service.