1 files changed, 3 insertions, 0 deletions
diff --git a/Lib/test/test_email/test_headerregistry.py b/Lib/test/test_email/test_headerregistry.py
index 7d64a38..55ecdea 100644
--- a/Lib/test/test_email/test_headerregistry.py
+++ b/Lib/test/test_email/test_headerregistry.py
@@ -1,6 +1,7 @@
 import datetime
 import textwrap
 import unittest
+import types
 from email import errors
 from email import policy
 from email.message import Message
@@ -235,6 +236,8 @@ class TestContentTypeHeader(TestHeaderBase):
         self.assertEqual(h.maintype, maintype)
         self.assertEqual(h.subtype, subtype)
         self.assertEqual(h.params, parmdict)
+        with self.assertRaises(TypeError):
+            h.params['abc'] = 'xyz'   # params is read-only.
         self.assertDefectsEqual(h.defects, defects)
         self.assertEqual(h, decoded)
         self.assertEqual(h.fold(policy=policy.default), folded)