diff --git a/ChangeLog b/ChangeLog
index d3ecfbc9e0..7460338e47 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Oct 25 13:33:58 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (io_cntl): F_DUPFD is platform dependent.
+
 Sun Oct 25 10:19:09 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/dl/handle.c (rb_dlhandle_close): fixed an invalid local
diff --git a/io.c b/io.c
index 426cba5a55..1488dc1ecc 100644
--- a/io.c
+++ b/io.c
@@ -7237,9 +7237,11 @@ io_cntl(int fd, unsigned long cmd, long narg, int io_p)
 # else
     retval = io_p?ioctl(fd, cmd, narg):fcntl(fd, (int)cmd, narg);
 # endif
+# if defined(F_DUPFD)
     if (!io_p && retval != -1 && cmd == F_DUPFD) {
         UPDATE_MAXFD(retval);
     }
+# endif
 #else
     if (!io_p) {
 	rb_notimplement();