This paper explores the relationship between self-organisation andtailored roles in large agile software development teams. The casestudy examines a Swedish IT company that has introduced the roleof “Security Master” in Scrum teams. The teams are developing avery large and secure 5G solution. Twenty semi-structuredinterviews were conducted and deductively analysed. The resultsshed light on the Security Master role, its need, responsibilities andimpact on secure coding. The paper concludes with a discussion oflessons learned and recommendations for future research in thecontext of large, security-sensitive projects.