.../Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php       | 5 ++---
 .../Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php   | 2 +-
 core/modules/system/src/Tests/System/AccessDeniedTest.php            | 3 +++
 core/modules/system/src/Tests/System/PageNotFoundTest.php            | 3 +++
 4 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php
index e306b38..623ba09 100644
--- a/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php
@@ -8,7 +8,6 @@
 namespace Drupal\Core\EventSubscriber;
 
 use Drupal\Core\Access\AccessManagerInterface;
-use Drupal\Core\Cache\CacheableDependencyInterface;
 use Drupal\Core\Cache\RefinableCacheableDependencyInterface;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Routing\AccessAwareRouterInterface;
@@ -52,7 +51,7 @@ class CustomPageExceptionHtmlSubscriber extends DefaultExceptionHtmlSubscriber {
    *   The redirect destination service.
    * @param \Symfony\Component\Routing\Matcher\UrlMatcherInterface $access_unaware_router
    *   A router implementation which does not check access.
-   * @param \Drupal\Core\Access\AccessManagerInterface
+   * @param \Drupal\Core\Access\AccessManagerInterface $access_manager
    *   The access manager.
    */
   public function __construct(ConfigFactoryInterface $config_factory, HttpKernelInterface $http_kernel, LoggerInterface $logger, RedirectDestinationInterface $redirect_destination, UrlMatcherInterface $access_unaware_router, AccessManagerInterface $access_manager) {
@@ -92,7 +91,7 @@ public function on404(GetResponseForExceptionEvent $event) {
    * Makes a subrequest to retrieve the custom error page.
    *
    * @param \Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent $event
-   *   The event to process
+   *   The event to process.
    * @param string $custom_path
    *   The custom path to which to make a subrequest for this error message.
    * @param int $status_code
diff --git a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
index bd9a6f3..153253a 100644
--- a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
@@ -118,7 +118,7 @@ public function on404(GetResponseForExceptionEvent $event) {
    * Makes a subrequest to retrieve the default error page.
    *
    * @param \Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent $event
-   *   The event to process
+   *   The event to process.
    * @param string $url
    *   The path/url to which to make a subrequest for this error message.
    * @param int $status_code
diff --git a/core/modules/system/src/Tests/System/AccessDeniedTest.php b/core/modules/system/src/Tests/System/AccessDeniedTest.php
index 100e974..db231c3 100644
--- a/core/modules/system/src/Tests/System/AccessDeniedTest.php
+++ b/core/modules/system/src/Tests/System/AccessDeniedTest.php
@@ -112,6 +112,9 @@ function testAccessDenied() {
     $this->assertText(t('Basic site settings'));
   }
 
+  /**
+   * Tests that an inaccessible custom 403 page falls back to the default.
+   */
   public function testAccessDeniedCustomPageWithAccessDenied() {
     // Sets up a 403 page not accessible by the anonymous user.
     $this->config('system.site')->set('page.403', '/system-test/custom-4xx')->save();
diff --git a/core/modules/system/src/Tests/System/PageNotFoundTest.php b/core/modules/system/src/Tests/System/PageNotFoundTest.php
index 17ad8d7..ffe985b 100644
--- a/core/modules/system/src/Tests/System/PageNotFoundTest.php
+++ b/core/modules/system/src/Tests/System/PageNotFoundTest.php
@@ -61,6 +61,9 @@ function testPageNotFound() {
     $this->assertText($this->adminUser->getUsername(), 'Found the custom 404 page');
   }
 
+  /**
+   * Tests that an inaccessible custom 404 page falls back to the default.
+   */
   public function testPageNotFoundCustomPageWithAccessDenied() {
     // Sets up a 404 page not accessible by the anonymous user.
     $this->config('system.site')->set('page.404', '/system-test/custom-4xx')->save();