diff -r 811ccdee6f87 Lib/test/test_os.py
--- a/Lib/test/test_os.py	Wed May 04 09:44:44 2016 +0300
+++ b/Lib/test/test_os.py	Sat May 07 17:53:37 2016 +0200
@@ -1314,7 +1314,9 @@
                         break
                 os.closerange(3, 256)
             with open({TESTFN!r}, 'rb') as f:
-                os.dup2(f.fileno(), fd)
+                new_fd = f.fileno()
+                if new_fd != fd:
+                    os.dup2(new_fd, fd)
                 sys.stdout.buffer.write(os.urandom(4))
                 sys.stdout.buffer.write(os.urandom(4))
             """.format(TESTFN=support.TESTFN)