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.