Hi, The code in construct() seems to surfer from copy/paste or merge error. It seems as though the following lines are duplicated in the else clause: void *const storage = ((converter::rvalue_from_python_storage<SP<T> >*)data)->storage.bytes; // Deal with the "None" case. if (data->convertible == source) new (storage) SP<T>(); Please take a look at: https://www.boost.org/doc/libs/1_82_0/boost/python/converter/shared_ptr_from... Ran.