diff --git a/Lib/test/test_email/test_message.py b/Lib/test/test_email/test_message.py
index 974b0ceaafbde4..ea30a94dfda24a 100644
--- a/Lib/test/test_email/test_message.py
+++ b/Lib/test/test_email/test_message.py
@@ -582,7 +582,7 @@ def _make_subtype_test_message(self, subtype):
             ('From', 'bar@foo.com'),
             ]
         if subtype != 'no_content':
-            ('content-shadow', 'Logrus'),
+            msg_headers.append(('content-shadow', 'Logrus'))
         msg_headers.append(('X-Random-Header', 'Corwin'))
         if subtype == 'text':
             payload = ''