diff -u b/core/lib/Drupal/Core/Controller/ExceptionController.php b/core/lib/Drupal/Core/Controller/ExceptionController.php
--- b/core/lib/Drupal/Core/Controller/ExceptionController.php
+++ b/core/lib/Drupal/Core/Controller/ExceptionController.php
@@ -338,10 +338,10 @@
    *   improvement as well.
    *
    * @param \Symfony\Component\Debug\Exception\FlattenException $exception
-   *  The flattened exception
+   *  The flattened exception.
    *
    * @return array
-   *   The exception
+   *   The exception that was contained within the FlattenException .
    */
   protected function decodeException(FlattenException $exception) {
     $message = $exception->getMessage();