diff --git a/Acl/CommentAclInterface.php b/Acl/CommentAclInterface.php
index df7818c63..0e4184014 100644
--- a/Acl/CommentAclInterface.php
+++ b/Acl/CommentAclInterface.php
@@ -41,7 +41,7 @@ public function canView(CommentInterface $comment);
      * Checks if the user can reply to the supplied 'parent' comment
      * or if not supplied, just the ability to reply.
      *
-     * @param CommentInterface $parent
+     * @param CommentInterface|null $parent
      *
      * @return bool
      */