diff -u b/core/lib/Drupal/Core/Cache/DatabaseBackend.php b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
--- b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
@@ -420,7 +420,7 @@
   }
 
   /**
-   * Ensures that cache IDs have a maximum length of 255 characters.
+   * Normalizes a cache ID in order to comply with database limitations.
    *
    * @param string $cid
    *   The passed in cache ID.