diff --git a/src/calibre/devices/mtp/windows/device.cpp b/src/calibre/devices/mtp/windows/device.cpp
index b55592eead..2389ac7dec 100644
--- a/src/calibre/devices/mtp/windows/device.cpp
+++ b/src/calibre/devices/mtp/windows/device.cpp
@@ -59,17 +59,12 @@ update_data(Device *self, PyObject *args) {
 // get_filesystem() {{{
 static PyObject*
 py_get_filesystem(Device *self, PyObject *args) {
-    PyObject *storage_id, *ret, *callback;
-    wchar_t *storage;
+    PyObject *callback;
+	wchar_raii storage;
 
-    if (!PyArg_ParseTuple(args, "OO", &storage_id, &callback)) return NULL;
+    if (!PyArg_ParseTuple(args, "O&O", py_to_wchar_no_none, &storage, &callback)) return NULL;
     if (!PyCallable_Check(callback)) { PyErr_SetString(PyExc_TypeError, "callback is not a callable"); return NULL; }
-    storage = unicode_to_wchar(storage_id);
-    if (storage == NULL) return NULL;
-
-    ret = wpd::get_filesystem(self->device, storage, self->bulk_properties, callback);
-    free(storage);
-    return ret;
+    return wpd::get_filesystem(self->device, storage.ptr(), self->bulk_properties, callback);
 } // }}}
 
 // get_file() {{{
diff --git a/src/calibre/utils/cpp_binding.h b/src/calibre/utils/cpp_binding.h
index 76f5f14508..f59eb66cfb 100644
--- a/src/calibre/utils/cpp_binding.h
+++ b/src/calibre/utils/cpp_binding.h
@@ -46,7 +46,7 @@ typedef generic_raii<PyObject*, python_object_destructor> pyobject_raii;
 
 
 static inline int
-py_to_wchar(PyObject *obj, wchar_raii *output) {
+py_to_wchar(PyObject *obj, wchar_t **output) {
 	if (!PyUnicode_Check(obj)) {
 		if (obj == Py_None) { return 1; }
 		PyErr_SetString(PyExc_TypeError, "unicode object expected");
@@ -54,18 +54,18 @@ py_to_wchar(PyObject *obj, wchar_raii *output) {
 	}
     wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
     if (!buf) { PyErr_NoMemory(); return 0; }
-	output->attach(buf);
+	*output = buf;
 	return 1;
 }
 
 static inline int
-py_to_wchar_no_none(PyObject *obj, wchar_raii *output) {
+py_to_wchar_no_none(PyObject *obj, wchar_t **output) {
 	if (!PyUnicode_Check(obj)) {
 		PyErr_SetString(PyExc_TypeError, "unicode object expected");
 		return 0;
 	}
     wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
     if (!buf) { PyErr_NoMemory(); return 0; }
-	output->attach(buf);
+	*output = buf;
 	return 1;
 }