diff --git a/ChangeLog b/ChangeLog
index 8a59bf9cca..72234c4cc4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Dec  5 18:13:39 2008  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* win32/win32.c (rb_w32_isatty): check whether fd is valid.
+
 Fri Dec  5 12:49:24 2008  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/win32.c (waitpid): fix bug of checking child slot.
diff --git a/win32/win32.c b/win32/win32.c
index 9d46bf0d6d..de90cfb144 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -4091,6 +4091,10 @@ rb_w32_unlink(const char *path)
 int
 rb_w32_isatty(int fd)
 {
+    // validate fd by using _get_osfhandle() because we cannot access _nhandle
+    if (_get_osfhandle(fd) == -1) {
+	return 0;
+    }
     if (!(_osfile(fd) & FOPEN)) {
 	errno = EBADF;
 	return 0;