diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
index 3aa74e3774c8c0..43a2219e067750 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -468,9 +468,9 @@ def test_stdout_flush_at_shutdown(self):
         rc, out, err = assert_python_failure('-c', code)
         self.assertEqual(b'', out)
         self.assertEqual(120, rc)
-        self.assertRegex(err.decode('ascii', 'ignore'),
-                r'Exception ignored on flushing sys\.stdout:\n'
-                r'OSError: .*')
+        self.assertIn(b'Exception ignored on flushing sys.stdout:\n'
+                      b'OSError: '.replace(b'\n', os.linesep.encode()),
+                      err)
 
     def test_closed_stdout(self):
         # Issue #13444: if stdout has been explicitly closed, we should