Agile processes potentially ease distributed software development by demanding regular communication and self-management of virtual team members. However, being designed for collocated teams, extensions to the regular process need to be made. We investigate critical areas of improvement based on a case of distributed Scrum involving two unaffiliated Austrian IT organizations that collaborate to build software. We identified eight critical areas for improvement originating from interviews, retrospective meetings and an in-depth case analysis. Key suggestions for practice include the establishment of long-lived single-site Scrum teams and the application of Behavior Driven Development (BDD) to make implicit requirement knowledge explicit and transparent to all of the distributed parties.