Get a large, I pretty sure they don't expand. And I think it's better if it's a tight fit, you don't really want the helmet to drop infront of your eyes do you when you are in the middle of something and can't see shit! I actually have the same helmet, large but that didn't fit my head but I just have an extra large head. I ended up shaving the inside walls out so it would fit . You should be fine though, unless you have a big head like me!