diff --git a/Lib/test/test_hmac.py b/Lib/test/test_hmac.py
index bc2e02528d..8e1a4a204c 100644
--- a/Lib/test/test_hmac.py
+++ b/Lib/test/test_hmac.py
@@ -389,6 +389,18 @@ def test_with_digestmod_no_default(self):
         with self.assertRaisesRegex(TypeError, r'required.*digestmod'):
             hmac.HMAC(key, msg=data, digestmod='')
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
+    def test_with_fallback(self):
+        cache = getattr(hashlib, '__builtin_constructor_cache')
+        try:
+            cache['foo'] = hashlib.sha256
+            hexdigest = hmac.digest(b'key', b'message', 'foo').hex()
+            expected = '6e9ef29b75fffc5b7abae527d58fdadb2fe42e7219011976917343065f58ed4a'
+            self.assertEqual(hexdigest, expected)
+        finally:
+            cache.pop('foo')
+
 
 class ConstructorTestCase(unittest.TestCase):