I assume this was supposed to be Py_ssize_t since there are no uses of plain ssize_t.
diff --git a/Include/longobject.h b/Include/longobject.h
index b7a29b5..9e87604 100644
--- a/Include/longobject.h
+++ b/Include/longobject.h
@@ -21,7 +21,7 @@
PyAPI_FUNC(PyObject *) PyLong_FromSsize_t(Py_ssize_t);
PyAPI_FUNC(PyObject *) PyLong_FromDouble(double);
PyAPI_FUNC(long) PyLong_AsLong(PyObject *);
-PyAPI_FUNC(ssize_t) PyLong_AsSsize_t(PyObject *);
+PyAPI_FUNC(Py_ssize_t) PyLong_AsSsize_t(PyObject *);
PyAPI_FUNC(size_t) PyLong_AsSize_t(PyObject *);
PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLong(PyObject *);
PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLongMask(PyObject *);