I don't think here is a problem. It crashes because you preallocate the type object in a wrong way. You should not just does a malloc and then passes it to the API. In this way, you are able to crash many APIs. For example, malloc a dictobject and then pass it to PyDict_SetItem could highly possibly crash. You should use PyDict_New to allocate the dictobject. Also here, you need to use PyType_GenericAlloc(&PyType_Type, 0) to allocate the type object, not just a malloc.