diff --git a/ChangeLog b/ChangeLog
index cc3c1fd405..9edf44e214 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,8 @@
 Wed Nov 21 16:13:37 2012  Koichi Sasada  <ko1@atdot.net>
 
-	* benchmark/bm_so_nsieve_bits.rb: add an encoding pragma.
+	* benchmark/bm_so_nsieve_bits.rb: add an encoding pragma because
+	  this benchmark using strings (literals) as binary sequence.
+	  Now, they are UTF-8 strings.
 
 Wed Nov 21 00:57:43 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>