diff --git a/core/lib/Drupal/Core/Config/Schema/Element.php b/core/lib/Drupal/Core/Config/Schema/Element.php
index 54a4882..86cf4de 100644
--- a/core/lib/Drupal/Core/Config/Schema/Element.php
+++ b/core/lib/Drupal/Core/Config/Schema/Element.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Config\Schema;
 
+use Drupal\Core\Config\TypedConfigManagerInterface;
 use Drupal\Core\TypedData\TypedData;
 use Drupal\Core\TypedData\TypedDataManagerInterface;
 
@@ -54,7 +55,7 @@ public function getTypedDataManager() {
    * @return $this
    */
   public function setTypedDataManager(TypedDataManagerInterface $typed_data_manager) {
-    assert('$typed_data_manager instanceof \Drupal\Core\Config\TypedConfigManagerInterface');
+    assert($typed_data_manager instanceof TypedConfigManagerInterface, '$typed_data_manager should be an instance of \Drupal\Core\Config\TypedConfigManagerInterface.');
     $this->typedDataManager = $typed_data_manager;
     return $this;
   }