diff --git a/core/lib/Drupal/Core/Config/ConfigManager.php b/core/lib/Drupal/Core/Config/ConfigManager.php
index fb8f658..eb59497 100644
--- a/core/lib/Drupal/Core/Config/ConfigManager.php
+++ b/core/lib/Drupal/Core/Config/ConfigManager.php
@@ -155,11 +155,15 @@ public function diff(StorageInterface $source_storage, StorageInterface $target_
     // Check for new or removed files.
     if ($source_data === array('false')) {
       // Added file.
-      $source_data = array($this->t('File added'));
+      // Cast the result of t() to a string, as the diff engine doesn't know
+      // about objects.
+      $source_data = array((string) $this->t('File added'));
     }
     if ($target_data === array('false')) {
       // Deleted file.
-      $target_data = array($this->t('File removed'));
+      // Cast the result of t() to a string, as the diff engine doesn't know
+      // about objects.
+      $target_data = array((string) $this->t('File removed'));
     }
 
     return new Diff($source_data, $target_data);