diff -r f9dd607dc04c Modules/_testcapimodule.c
--- a/Modules/_testcapimodule.c	Tue Jan 03 02:01:42 2017 +0100
+++ b/Modules/_testcapimodule.c	Tue Jan 03 02:30:42 2017 +0100
@@ -4039,6 +4039,60 @@ dict_get_version(PyObject *self, PyObjec
     return PyLong_FromUnsignedLongLong((unsigned PY_LONG_LONG)version);
 }
 
+static Py_uintptr_t compute_stack_start;
+
+static PyObject*
+compute_stacksize(PyObject *self, PyObject *args)
+{
+    PyObject *func, *n2, *res;
+    Py_ssize_t n;
+    Py_uintptr_t stack;
+    size_t stack_size;
+
+    if (!PyArg_ParseTuple(args, "On", &func, &n)) {
+        return NULL;
+    }
+
+    stack = (Py_uintptr_t)&func;
+    if (stack > compute_stack_start) {
+        stack_size = stack - compute_stack_start;
+    }
+    else {
+        stack_size = compute_stack_start - stack;
+    }
+
+    if (n == 0) {
+        return PyLong_FromSize_t(stack_size);
+    }
+
+    n2 = PyLong_FromSsize_t(n - 1);
+    if (n2 == NULL) {
+        return NULL;
+    }
+
+    res = PyObject_CallFunctionObjArgs(func, func, n2, NULL);
+    Py_DECREF(n2);
+    return res;
+}
+
+static PyObject*
+pyobjectl_callfunctionobjargs_stacksize(PyObject *self, PyObject *arg)
+{
+    PyMethodDef meth = {"compute_stacksize", compute_stacksize, METH_VARARGS};
+    PyObject *func, *res;
+
+    compute_stack_start = (Py_uintptr_t)&meth;
+    func = PyCFunction_NewEx(&meth, self, NULL);
+    if (func == NULL) {
+        return NULL;
+    }
+
+    res = PyObject_CallFunctionObjArgs(func, func, arg, NULL);
+    Py_DECREF(func);
+
+    return res;
+}
+
 
 static PyMethodDef TestMethods[] = {
     {"raise_exception",         raise_exception,                 METH_VARARGS},
@@ -4244,6 +4298,8 @@ static PyMethodDef TestMethods[] = {
     {"tracemalloc_untrack", tracemalloc_untrack, METH_VARARGS},
     {"tracemalloc_get_traceback", tracemalloc_get_traceback, METH_VARARGS},
     {"dict_get_version", dict_get_version, METH_VARARGS},
+    {"pyobjectl_callfunctionobjargs_stacksize",
+     pyobjectl_callfunctionobjargs_stacksize, METH_O},
     {NULL, NULL} /* sentinel */
 };