diff --git a/ChangeLog b/ChangeLog
index d02d3b491b..da3077f5c8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,7 +12,7 @@ Fri Feb 20 23:28:11 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
 Thu Feb 19 22:59:09 2009  Tanaka Akira  <akr@fsij.org>
 
 	* ext/socket/ancdata.c (make_io_for_unix_rights): cmsg_len may be
-	  bigger than msg_controllen.
+	  bigger than msg_controllen on 4.4BSD at least.
 	  freeze unix_rights array.
 
 Thu Feb 19 22:17:38 2009  Tanaka Akira  <akr@fsij.org>