diff --git a/modules/authcache_p13n/includes/AuthcacheP13nDefaultCoreService.inc b/modules/authcache_p13n/includes/AuthcacheP13nDefaultCoreService.inc
index 13936f4..9a08ee9 100644
--- a/modules/authcache_p13n/includes/AuthcacheP13nDefaultCoreService.inc
+++ b/modules/authcache_p13n/includes/AuthcacheP13nDefaultCoreService.inc
@@ -12,7 +12,7 @@ class AuthcacheP13nDefaultCoreService implements AuthcacheP13nCoreServiceInterfa
    * {@inheritdoc}
    */
   public function drupalAddHttpHeader($name, $value, $append = FALSE) {
-    drupal_add_http_header($name, $value, $append = FALSE);
+    drupal_add_http_header($name, $value, $append);
   }
 
   /**