The main focus of the requirements engineering (RE) literature has been on the technical aspects related to the RE projects. Furthermore, research has mainly focused on the specific methods for collecting the requirements for an information system. To fill this gap, this paper studies the contribution of social factors, such as social ties, knowledge sharing and flexibility, to successful collaboration in RE teams. Data were collected from a successful RE and development project in a public sector company in Finland. The results suggest that human-related issues, such as flexibility and transactive memory, were important for collaborative work in the RE team studied. The paper concludes by discussing the implications for theory and suggesting practical guidelines to enhance collaborative work in RE teams.