diff --git a/ChangeLog b/ChangeLog
index 256b71ff9b..2ed78e9c76 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Sep  9 13:50:05 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* doc/extension.rdoc, doc/extension.ja.rdoc: fix file name.
+	  pointed out by @takkanm in the RubyKaigi talk.
+
 Fri Sep  9 13:14:53 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* News: Announcing update to Unicode version 9.0.0 [ci skip]
diff --git a/doc/extension.ja.rdoc b/doc/extension.ja.rdoc
index 6ecb78cb79..1537054b6c 100644
--- a/doc/extension.ja.rdoc
+++ b/doc/extension.ja.rdoc
@@ -1,4 +1,4 @@
-# README.EXT.ja -  -*- RDoc -*- created at: Mon Aug  7 16:45:54 JST 1995
+# extension.ja.rdoc -  -*- RDoc -*- created at: Mon Aug  7 16:45:54 JST 1995
 
 Rubyの拡張ライブラリの作り方を説明します．
 
diff --git a/doc/extension.rdoc b/doc/extension.rdoc
index 1e157f824a..28052708e2 100644
--- a/doc/extension.rdoc
+++ b/doc/extension.rdoc
@@ -1,4 +1,4 @@
-# README.EXT -  -*- RDoc -*- created at: Mon Aug  7 16:45:54 JST 1995
+# extension.rdoc -  -*- RDoc -*- created at: Mon Aug  7 16:45:54 JST 1995
 
 This document explains how to make extension libraries for Ruby.