@@ -103,6 +103,7 @@ PyCFunction_Call(PyObject *func, PyObject *args, PyObject *kwds)
     else if (flags == METH_FASTCALL) {
         PyObject **stack = &PyTuple_GET_ITEM(args, 0);
         Py_ssize_t nargs = PyTuple_GET_SIZE(args);
+        STACKLESS_PROMOTE_ALL();
         res = _PyCFunction_FastCallDict(func, stack, nargs, kwds);
     }
     else {
@@ -259,6 +260,7 @@ _PyCFunction_FastCallDict(PyObject *func_obj, PyObject **args, Py_ssize_t nargs,
             return NULL;
         }
 
+        STACKLESS_PROMOTE_FLAG(PyCFunction_GET_FLAGS(func) & METH_STACKLESS);
         result = (*fastmeth) (self, stack, nargs, kwnames);
         if (stack != args) {
             PyMem_Free(stack);
 
@@ -9,6 +9,10 @@ What's New in Stackless 3.X.X?
 
 *Release date: 20XX-XX-XX*
 
+- https://github.com/stackless-dev/stackless/issues/133
+  WARNING: C-extension modules written for Stackless Python must be recompiled
+  for Stackless Python 3.6, because definition of METH_STACKLESS changed.
+
 - https://github.com/stackless-dev/stackless/issues/140
   Fix bugs in prickelpit.c unwrap_frame_arg() and slp_find_execname().
Original file line number	Diff line number	Diff line change
@@ -103,6 +103,7 @@ PyCFunction_Call(PyObject func, PyObject args, PyObject *kwds)
103	103	else if (flags == METH_FASTCALL) {
104	104	PyObject **stack = &PyTuple_GET_ITEM(args, 0);
105	105	Py_ssize_t nargs = PyTuple_GET_SIZE(args);
	106	+ STACKLESS_PROMOTE_ALL();
106	107	res = _PyCFunction_FastCallDict(func, stack, nargs, kwds);
107	108	}
108	109	else {
@@ -259,6 +260,7 @@ _PyCFunction_FastCallDict(PyObject func_obj, PyObject *args, Py_ssize_t nargs,
259	260	return NULL;
260	261	}
261	262
	263	+ STACKLESS_PROMOTE_FLAG(PyCFunction_GET_FLAGS(func) & METH_STACKLESS);
262	264	result = (*fastmeth) (self, stack, nargs, kwnames);
263	265	if (stack != args) {
264	266	PyMem_Free(stack);