diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 8b12b42ccfa..32dd8e43920 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1350,7 +1350,8 @@ function drupal_serve_page_from_cache(stdClass $cache) {
   // max-age > 0, allowing the page to be cached by external proxies, when a
   // session cookie is present unless the Vary header has been replaced or
   // unset in hook_boot().
-  $max_age = !isset($_COOKIE[session_name()]) || isset($hook_boot_headers['vary']) ? variable_get('page_cache_maximum_age', 0) : 0;
+  $config = config('system.performance');
+  $max_age = !isset($_COOKIE[session_name()]) || isset($hook_boot_headers['vary']) ? $config->get('page_cache_maximum_age') : 0;
   $default_headers['Cache-Control'] = 'public, max-age=' . $max_age;
 
   // Entity tag should change if the output changes.