[Adam]

There aren't a lot of good options for discussing rules during a game. If he's right or if he's wrong, you've got to go with it.
How he accepts your approach will depend on a few things, so I can't tell you how he'll take it. It's always (in my opinion) best to ask bring it up to him in a casual social setting, if you have the opportunity. Even before a game can sometimes be a poor way to start off a game.

I know what you're saying, though, in wanting the call to be right.

Can I ask what rule he got wrong?