diff --git a/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsInterface.php b/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsInterface.php
index ae5f0bd..88e032b 100644
--- a/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsInterface.php
+++ b/core/lib/Drupal/Core/Config/Entity/ThirdPartySettingsInterface.php
@@ -44,7 +44,7 @@ public function setThirdPartySetting($module, $key, $value);
    * @return mixed
    *   The value.
    */
-  public function getThirdPartySetting($module, $key, $default);
+  public function getThirdPartySetting($module, $key, $default = NULL);
 
   /**
    * Unsets a third-party setting.