diff --git a/Lib/test/test_structseq.py b/Lib/test/test_structseq.py
@@ -122,5 +122,17 @@ def test_extended_getslice(self):
                    self.assertEqual(list(t[start:stop:step]),
                                     L[start:stop:step])

if __name__ == "__main__":
    unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-03-03-19-04-23.bpo-42128.VouZjn.rst b/Misc/NEWS.d/next/Core and Builtins/2021-03-03-19-04-23.bpo-42128.VouZjn.rst
@@ -0,0 +1,2 @@
diff --git a/Objects/structseq.c b/Objects/structseq.c
@@ -15,6 +15,7 @@
static const char visible_length_key[] = "n_sequence_fields";
static const char real_length_key[] = "n_fields";
static const char unnamed_fields_key[] = "n_unnamed_fields";

/* Fields with this name have only a field index, not a field name.
   They are only allowed for indices < n_visible_fields. */
@@ -399,7 +400,40 @@ initialize_structseq_dict(PyStructSequence_Desc *desc, PyObject* dict,
    SET_DICT_FROM_SIZE(visible_length_key, desc->n_in_sequence);
    SET_DICT_FROM_SIZE(real_length_key, n_members);
    SET_DICT_FROM_SIZE(unnamed_fields_key, n_unnamed_members);
    return 0;
}

static void