diff --git a/ChangeLog b/ChangeLog
index 7798f8064f..46cbabc601 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Thu Jan 22 15:54:02 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* include/ruby/win32.h, win32/win32.c (rb_w32_is_valid_fd): new function
+	  to validate fd.
+
+	* io.c (rb_io_initialize): check fd with above function.
+
 Thu Jan 22 14:53:29 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* test/ruby/test_process.rb (MANDATORY_ENVS): needs RUBYLIB to run
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index 46388a3ae2..1bbe69e69c 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -214,6 +214,7 @@ extern int    WSAAPI rb_w32_connect(int, const struct sockaddr *, int);
 extern void   rb_w32_fdset(int, fd_set*);
 extern void   rb_w32_fdclr(int, fd_set*);
 extern int    rb_w32_fdisset(int, fd_set*);
+extern int    rb_w32_is_valid_fd(int);
 extern int    WSAAPI rb_w32_select(int, fd_set *, fd_set *, fd_set *, struct timeval *);
 extern int    WSAAPI rb_w32_getpeername(int, struct sockaddr *, int *);
 extern int    WSAAPI rb_w32_getsockname(int, struct sockaddr *, int *);
diff --git a/io.c b/io.c
index 5555de7c26..c62af6ee35 100644
--- a/io.c
+++ b/io.c
@@ -5971,13 +5971,15 @@ rb_io_initialize(int argc, VALUE *argv, VALUE io)
     fd = NUM2INT(fnum);
     if (fstat(fd, &st) == -1) rb_sys_fail(0);
     UPDATE_MAXFD(fd);
-    if (NIL_P(vmode)) {
 #if defined(HAVE_FCNTL) && defined(F_GETFL)
+    if (NIL_P(vmode)) {
         oflags = fcntl(fd, F_GETFL);
         if (oflags == -1) rb_sys_fail(0);
         fmode = rb_io_oflags_fmode(oflags);
-#endif
     }
+#elif defined(_WIN32)
+    if (rb_w32_is_valid_fd(fd)) rb_sys_fail(0);
+#endif
     MakeOpenFile(io, fp);
     fp->fd = fd;
     fp->mode = fmode;
diff --git a/win32/win32.c b/win32/win32.c
index b948fe0d77..ba8a96e82c 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -1836,6 +1836,15 @@ rb_w32_open_osfhandle(intptr_t osfhandle, int flags)
 }
 #endif
 
+int
+rb_w32_is_valid_fd(int fd)
+{
+    if (_get_osfhandle(fd) == -1)
+	return -1;
+    else
+	return 0;
+}
+
 #undef getsockopt
 
 static int