In Objects/typeobject.c, the PyMemberDefs for __flags__, __weakrefoffset__, and __dictoffset__ all use T_LONG:

    {"__flags__", T_LONG, offsetof(PyTypeObject, tp_flags), READONLY},
    {"__weakrefoffset__", T_LONG,
     offsetof(PyTypeObject, tp_weaklistoffset), READONLY},
    ...
    {"__dictoffset__", T_LONG,
     offsetof(PyTypeObject, tp_dictoffset), READONLY},

    {"__weakrefoffset__", T_LONG,
     offsetof(PyTypeObject, tp_weaklistoffset), READONLY},

but in Include/object.h or Include/cpython/object.h, the corresponding struct members have types unsigned long, Py_ssize_t, and Py_ssize_t respectively:

    /* Flags to define presence of optional/expanded features */
    unsigned long tp_flags;
    ...
    /* weak reference enabler */
    Py_ssize_t tp_weaklistoffset;
    ...
    Py_ssize_t tp_dictoffset;

These uses of T_LONG should be changed to T_ULONG and T_PYSSIZE_T.

This was checked on 3.7.3 and master.