diff --git a/ChangeLog b/ChangeLog
index 7209880c0f..00413366a6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun May 22 04:11:12 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* thread.c (Init_Thread): add a code comment why the meaningless
+	  line is necessary.
+
 Sun May 22 01:35:12 2011  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* ext/date/date_core.c: modified documentation.
diff --git a/thread.c b/thread.c
index 23ed2bc07f..cf7affa424 100644
--- a/thread.c
+++ b/thread.c
@@ -4694,6 +4694,7 @@ Init_Thread(void)
 
     rb_thread_create_timer_thread();
 
+    /* suppress warnings on cygwin, mingw and mswin.*/
     (void)native_mutex_trylock;
 }