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
@@ -67,6 +67,9 @@
    *   The flattened exception.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   A response object to be sent to the server.
    */
   public function on405Html(FlattenException $exception, Request $request) {
     return new Response('Method Not Allowed', 405);
@@ -79,6 +82,9 @@
    *   The flattened exception.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   A response object to be sent to the server.
    */
   public function on403Html(FlattenException $exception, Request $request) {
     $system_path = $request->attributes->get('_system_path');
@@ -134,6 +140,9 @@
    *   The flattened exception.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   A response object to be sent to the server.
    */
   public function on404Html(FlattenException $exception, Request $request) {
     watchdog('page not found', check_plain($request->attributes->get('_system_path')), NULL, WATCHDOG_WARNING);
@@ -206,6 +215,9 @@
    *   Metadata about the exception that was thrown.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   A response object to be sent to the server.
    */
   public function on500Html(FlattenException $exception, Request $request) {
     $error = $this->decodeException($exception);
@@ -274,6 +286,9 @@
    *   The flattened exception.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\JsonResponse
+   *   A JSON response object to be sent to the server.
    */
   public function on403Json(FlattenException $exception, Request $request) {
     $response = new JsonResponse();
@@ -288,6 +303,9 @@
    *   The flattened exception.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\JsonResponse
+   *   A JSON response object to be sent to the server.
    */
   public function on404Json(FlattenException $exception, Request $request) {
     $response = new JsonResponse();
@@ -302,6 +320,9 @@
    *   The flattened exception.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The request object that triggered this exception.
+   *
+   * @return \Symfony\Component\HttpFoundation\JsonResponse
+   *   A JSON response object to be sent to the server.
    */
   public function on405Json(FlattenException $exception, Request $request) {
     $response = new JsonResponse();
@@ -318,7 +339,9 @@
    *
    * @param \Symfony\Component\Debug\Exception\FlattenException $exception
    *  The flattened exception
+   *
    * @return array
+   *   The exception
    */
   protected function decodeException(FlattenException $exception) {
     $message = $exception->getMessage();
@@ -373,7 +396,7 @@
    * @param $backtrace
    *   A standard PHP backtrace.
    *
-   * @return
+   * @return array
    *   An associative array with keys 'file', 'line' and 'function'.
    */
   protected function getLastCaller($backtrace) {