diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index 230dbf4..c64ac19 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -454,7 +454,8 @@
     type2test = bytes
 
     def test_buffer_is_readonly(self):
-        with open(sys.stdin.fileno(), "rb", buffering=0) as f:
+        fd = os.dup(sys.stdin.fileno())
+        with open(fd, "rb", buffering=0) as f:
             self.assertRaises(TypeError, f.readinto, b"")