In mature and highly regulated markets, digital entrepreneurship may demand institutional changes to flourish. This paper aims to analyze institutional changes associated with the entry of new digital entrepreneurs (fintechs) into a national payment system. To achieve this goal, we conducted a case study in the Brazilian mobile payment system, with data collected from multiple sources, such as interviews with fintech entrepreneurs, document analysis, a survey with 580 users and non-users of mobile payments, and participant observations during a fintech summit. The Institutional Theory supported the understanding of institutional changes regarding the regulatory, normative, and cultural/cognitive pillars of the mobile payment system needed to support the new entrants (fintechs). The institutional work performed to carry on these changes is also analyzed.