diff --git a/ChangeLog b/ChangeLog
index 59cd9dc300..321e6035da 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Tue Dec 18 18:57:58 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+
+	* io.c (rb_io_wait_writable): don't use rb_thread_wait_fd()
+	  because it is for waiting until io readable.
+
+	* io.c (rb_io_wait_writable): always use rb_thread_fd_writable()
+	  instaed of bare rb_wait_for_single_fd(). we shouldn't ignore
+	  return value.
+	* io.c (rb_io_wait_readable): ditto. always use rb_thread_wait_fd().
+
 Tue Dec 18 18:55:33 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread.c (rb_thread_wait_fd_rw): fix infinite loop bug.
diff --git a/io.c b/io.c
index 3047da4380..25680cf83e 100644
--- a/io.c
+++ b/io.c
@@ -1050,14 +1050,11 @@ rb_io_wait_readable(int f)
 #if defined(ERESTART)
       case ERESTART:
 #endif
-	rb_thread_wait_fd(f);
-	return TRUE;
-
       case EAGAIN:
 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
       case EWOULDBLOCK:
 #endif
-	rb_wait_for_single_fd(f, RB_WAITFD_IN, NULL);
+	rb_thread_wait_fd(f);
 	return TRUE;
 
       default:
@@ -1076,14 +1073,11 @@ rb_io_wait_writable(int f)
 #if defined(ERESTART)
       case ERESTART:
 #endif
-	rb_thread_wait_fd(f);
-	return TRUE;
-
       case EAGAIN:
 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
       case EWOULDBLOCK:
 #endif
-	rb_wait_for_single_fd(f, RB_WAITFD_OUT, NULL);
+	rb_thread_fd_writable(f);
 	return TRUE;
 
       default: