diff --git a/ChangeLog b/ChangeLog
index 69e08ece20..3a5a649dfe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat May  7 22:43:48 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* thread.c (rb_fd_zero): remove redundant zero fill.
+
 Sat May  7 22:38:04 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread.c (rb_fd_init): remove volatile qualifier.
diff --git a/thread.c b/thread.c
index 55236b7f8e..182feb31a1 100644
--- a/thread.c
+++ b/thread.c
@@ -2350,10 +2350,8 @@ rb_fd_term(rb_fdset_t *fds)
 void
 rb_fd_zero(rb_fdset_t *fds)
 {
-    if (fds->fdset) {
+    if (fds->fdset)
 	MEMZERO(fds->fdset, fd_mask, howmany(fds->maxfd, NFDBITS));
-	FD_ZERO(fds->fdset);
-    }
 }
 
 static void