diff --git a/editors/protobuf-mode.el b/editors/protobuf-mode.el
index d3bdcded70..f73d4b2b45 100644
--- a/editors/protobuf-mode.el
+++ b/editors/protobuf-mode.el
@@ -1,4 +1,4 @@
-;;; protobuf-mode.el --- major mode for editing protocol buffers.
+;;; protobuf-mode.el --- major mode for editing protocol buffers.  -*- lexical-binding: t; -*-
 
 ;; Author: Alexandre Vassalotti <alexandre@peadrop.com>
 ;; Created: 23-Apr-2009