diff --git a/ChangeLog b/ChangeLog
index c7ba7b8580..78a2fe4253 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,7 +10,8 @@ Sun Dec  8 20:26:54 2013  Yutaka Kanemoto  <kanemoto@ruby-lang.org>
 Sun Dec  8 20:21:00 2013  Kenta Murata  <mrkn@mrkn.jp>
 
 	* bigdecimal.c (BigDecimal_coerce): convert a Float to a BigDecimal instead
-	  of converting the receiver to a Float.
+	  of converting the receiver to a Float.  The reason is there are BigDecimal
+	  instances with precisions that is smaller than the Float's precision.
 	  [ruby-core:58756] [Bug #9192]
 
 	* test/bigdecimal/test_bigdecimal.rb: add tests for the above change.