diff --git a/ChangeLog b/ChangeLog
index 4db628d44e..14728051ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Nov 14 16:43:02 2015  Tanaka Akira  <akr@fsij.org>
+
+	* lib/open3.rb: Specify frozen_string_literal: true.
+
 Sat Nov 14 05:04:09 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* node.h: remove old comments.
diff --git a/lib/open3.rb b/lib/open3.rb
index 58245100b4..3c9d450737 100644
--- a/lib/open3.rb
+++ b/lib/open3.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # = open3.rb: Popen, but with stderr, too
 #
diff --git a/test/test_open3.rb b/test/test_open3.rb
index ca710bc0ba..d52ab6a9bf 100644
--- a/test/test_open3.rb
+++ b/test/test_open3.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test/unit'
 require 'open3'