I would mention it to him, but in a light-hearted manner, like “Not a big deal, but this thing that was added, do you remember?” If he says no, just say “You told me to add it,” chuckling in a “nice ribbing sort of way”. If your boss likes you, he will take the light-hearted comment in a good way but also acknowledge his mistake. In that way, it saves both your butt and his face.