1 files changed, 4 insertions, 2 deletions
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;