Video game modding is a form of fan productivity in contemporary participatory culture. We see modding as an important way in which modders experience and conceptualize their work. By focusing on modding in a free and open source software video game, we analyze the practice of modding and the way it changes modders' relationship with their object of interest. The modders' involvement is not always associated with fun and creativity. Indeed, activities such as play testing often undermine these dimensions of modding. We present a case study of modding that is based on ethnographic research done for The Battle for Wesnoth, a free and open source software strategy video game entirely developed by a community of volunteers.