diff --git a/ChangeLog b/ChangeLog
index a7ab67f432..0e531ed4f7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Apr 25 23:50:08 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (ruby_dup): update max fd.
+
 Sun Apr 25 21:56:49 2010  Shugo Maeda  <shugo@ruby-lang.org>
 
 	* lib/net/imap.rb (fetch_internal): do not quote message data item
diff --git a/io.c b/io.c
index 2eba0ec6d4..30150fc507 100644
--- a/io.c
+++ b/io.c
@@ -507,6 +507,7 @@ ruby_dup(int orig)
 	    rb_sys_fail(0);
 	}
     }
+    UPDATE_MAXFD(fd);
     return fd;
 }