diff --git a/ChangeLog b/ChangeLog
index f6f302c22b..2dec5dc70e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jan 27 21:03:45 2016  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
+
+	* test/-ext-/string/test_capacity.rb: Added missing library. 
+
 Wed Jan 27 18:53:40 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* enc/unicode.c: Fixed bit mask in macro OnigCodePointCount
diff --git a/test/-ext-/string/test_capacity.rb b/test/-ext-/string/test_capacity.rb
index b4e4fb7c02..54f3caf32e 100644
--- a/test/-ext-/string/test_capacity.rb
+++ b/test/-ext-/string/test_capacity.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 require 'test/unit'
 require '-test-/string'
+require 'rbconfig/sizeof'
 
 class Test_StringCapacity < Test::Unit::TestCase
   def test_capacity_embeded