In the field of business process management, deadlocks describe a situation where a workflow execution is blocked and cannot be completed. We speak of policy-based deadlocks if such a situation is caused by unsatisfiable resource requirements due to security constraints specified as part of the business process. In this paper we propose a method to avoid policy-based deadlocks by analyzing a workflow's security constraints, determine the minimal required number of users, and provide an optimal user-activity assignment for a deadlock-free workflow execution. We will finally validate our proposed approach by applying it to a real-world scenario.