diff --git a/tests/test_cli.py b/tests/test_cli.py

index e53e209..3828870 100644

--- a/tests/test_cli.py

+++ b/tests/test_cli.py

@@ -58,7 +58,7 @@ class TestConvert(TestCase):

         self.assertIn('underscore-emphasis', message)

         self.assertIn('anonymous-references', message)

         self.assertIn('inline-math', message)

-        self.assertIn('optional arguments:', message)

+        self.assertRegex(message, r'option(s|al arguments):')

     def test_parse_file(self):

         output = parse_from_file(test_md)