diff --git a/ChangeLog b/ChangeLog
index 43f22d94dd..cc7a64b250 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Feb  3 12:26:35 2015  Katsuhiko Nishimra  <ktns.87@gmail.com>
+
+	* lib/mkmf.rb (configuration): set the default cxxflags, which is
+	  referred from the default CXXFLAGS, for extension libraries.
+	  [Fix GH-823]
+
 Tue Feb  3 05:52:00 2015  Aman Gupta <ruby@tmm1.net>
 
 	* gc.c (rb_objspace_free): cause rb_bug if lazy sweep is in progress
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index e7c466f6fe..e8750e4f9d 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1928,6 +1928,7 @@ COUTFLAG = #{COUTFLAG}$(empty)
 
 RUBY_EXTCONF_H = #{$extconf_h}
 cflags   = #{CONFIG['cflags']}
+cxxflags = #{CONFIG['cxxflags']}
 optflags = #{CONFIG['optflags']}
 debugflags = #{CONFIG['debugflags']}
 warnflags = #{$warnflags}