Our research concerns the customer-supplier relationship in the development of breakthrough innovations in software design. In the work of Freeman (1982), the taking into account of customers' needs is highlighted as a key factor of success of innovation processes. Yet the first users are likely to orientate the innovation process towards very specific needs. To what extent does the designer of an innovation have to satisfy these needs, while developing a product intended for a significant number of customers? The author examines the case of a software designer, in which he focuses on a lead user whose usage skills contributed towards the design of the innovation.