diff --git a/core/modules/page_cache/src/StackMiddleware/PageCache.php b/core/modules/page_cache/src/StackMiddleware/PageCache.php
index 76852e3..f7432c2 100644
--- a/core/modules/page_cache/src/StackMiddleware/PageCache.php
+++ b/core/modules/page_cache/src/StackMiddleware/PageCache.php
@@ -230,8 +230,9 @@ protected function fetch(Request $request, $type = self::MASTER_REQUEST, $catch
       return $response;
     }
 
-    $max_age = $response->getCacheableMetadata()->getCacheMaxAge();
-    $expire = ($max_age === Cache::PERMANENT) ? Cache::PERMANENT : (int) $request->server->get('REQUEST_TIME') + $max_age;
+    // Use the actual timestamp from an Expires header, if available.
+    $date = $response->getExpires()->getTimestamp();
+    $expire = ($date > time()) ? $date : Cache::PERMANENT;
     $this->set($request, $response, $expire, $response->getCacheableMetadata()->getCacheTags());
 
     // Mark response as a cache miss.