diff --git a/tests/mail/tests.py b/tests/mail/tests.py
index 5cc9148d5b..5cf7bac2da 100644
--- a/tests/mail/tests.py
+++ b/tests/mail/tests.py
@@ -11,6 +11,7 @@ from datetime import datetime, timezone
 from email import message_from_binary_file
 from email import message_from_bytes as _message_from_bytes
 from email import policy
+from email.errors import HeaderWriteError
 from email.headerregistry import Address
 from email.message import EmailMessage as PyEmailMessage
 from email.message import Message as PyMessage
@@ -3145,17 +3146,25 @@ class SMTPBackendTests(BaseEmailBackendTests, SMTPBackendTestsBase):
         )
 
     def test_rejects_non_ascii_local_part(self):
-        """
-        The SMTP EmailBackend does not currently support non-ASCII local-parts.
-        (That would require using the RFC 6532 SMTPUTF8 extension.) #35713.
-        """
+        # The SMTP EmailBackend must work around invalid email encoding caused
+        # by https://github.com/python/cpython/issues/122476 (#35713).
+        try:
+            # Detect fix for CPython issue gh-122476.
+            message = PyEmailMessage()
+            message["To"] = "nø@example.dk"
+            message.as_bytes()
+        except HeaderWriteError:
+            # PY315: Error from Python email generator.
+            msg = "Non-ASCII local-part 'nø' is invalid"
+        else:
+            # Python <=3.14: Error from smtp.EmailBackend.prep_address().
+            msg = (
+                "Invalid address 'nø@example.dk': local-part contains "
+                "non-ASCII characters"
+            )
         backend = smtp.EmailBackend()
-        backend.connection = mock.Mock(spec=object())
         email = EmailMessage(to=["nø@example.dk"])
-        with self.assertRaisesMessage(
-            ValueError,
-            "Invalid address 'nø@example.dk': local-part contains non-ASCII characters",
-        ):
+        with self.assertRaisesMessage((ValueError, HeaderWriteError), msg):
             backend.send_messages([email])
 
     def test_prep_address_without_force_ascii(self):