diff --git a/lisp/tooltip.el b/lisp/tooltip.el
index 5f5a4788b26..00d21666c23 100644
--- a/lisp/tooltip.el
+++ b/lisp/tooltip.el
@@ -1,4 +1,4 @@
-;;; tooltip.el --- show tooltip windows
+;;; tooltip.el --- show tooltip windows  -*- lexical-binding:t -*-
 
 ;; Copyright (C) 1997, 1999-2020 Free Software Foundation, Inc.