diff -r ad91465a3c66 Objects/abstract.c
--- a/Objects/abstract.c	Mon Jan 23 12:34:00 2017 +0100
+++ b/Objects/abstract.c	Tue Jan 24 09:46:06 2017 +0100
@@ -2413,7 +2413,9 @@ PyObject *
     for (i = 0; i < nkwargs; i++) {
         PyObject *key = PyTuple_GET_ITEM(kwnames, i);
         PyObject *value = *values++;
-        assert(PyUnicode_CheckExact(key));
+        /* keys must be strings, but it is the responsability of the final
+           function to implement this check. For example, PyArg_ParseXXX()
+           functions implement this check */
         assert(PyDict_GetItem(kwdict, key) == NULL);
         if (PyDict_SetItem(kwdict, key, value)) {
             Py_DECREF(kwdict);