diff --git a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
index 747262c..431eb06 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
@@ -156,6 +156,7 @@ public function onRespond(FilterResponseEvent $event) {
       $response_cacheability = $response->getCacheableMetadata();
       $response->headers->set('X-Drupal-Cache-Tags', implode(' ', $response_cacheability->getCacheTags()));
       $response->headers->set('X-Drupal-Cache-Contexts', implode(' ', $this->cacheContextsManager->optimizeTokens($response_cacheability->getCacheContexts())));
+      $response->headers->set('X-Drupal-Cache-Max-Age', $response_cacheability->getCacheMaxAge());
     }
 
     $is_cacheable = ($this->requestPolicy->check($request) === RequestPolicyInterface::ALLOW) && ($this->responsePolicy->check($response, $request) !== ResponsePolicyInterface::DENY);
diff --git a/sites/default/default.services.yml b/sites/default/default.services.yml
index e1bbbc7..816df3d 100644
--- a/sites/default/default.services.yml
+++ b/sites/default/default.services.yml
@@ -118,7 +118,8 @@ parameters:
   # Cacheability debugging:
   #
   # Responses with cacheability metadata (CacheableResponseInterface instances)
-  # get X-Drupal-Cache-Tags and X-Drupal-Cache-Contexts headers.
+  # get X-Drupal-Cache-Tags, X-Drupal-Cache-Contexts and X-Drupal-Max-Age
+  # headers.
   #
   # For more information about debugging cacheable responses, see
   # https://www.drupal.org/developing/api/8/response/cacheable-response-interface