A no-op change.  It looks like this call was not meant to be a recursive
call, but just call the helper (which the recursive call ends up doing).
diff --git a/Objects/setobject.c b/Objects/setobject.c
index 00cabe6..56f3087 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -1858,7 +1858,7 @@
         tmpkey = make_new_set(&PyFrozenSet_Type, key);
         if (tmpkey == NULL)
             return -1;
-        rv = set_contains(so, tmpkey);
+        rv = set_contains_key(so, tmpkey);
         Py_DECREF(tmpkey);
     }
     return rv;