Adaptability has become one of the major research topics in the area of workflow management. Today's workflow management systems have problems dealing with both ad-hoc changes and evolutionary changes. As a result, the workflow management system is not used to support dynamically changing workflow processes or the workflow process is supported in a rigid manner, i.e., changes are not allowed or handled outside of the workflow management system. In this paper, we focus on a notorious problem caused by workflow change: the dynamic change bug (Ellis et al.; Proceedings of the Conference on Organizational Computing Systems, Milpitas, California, ACM SIGOIS, ACM Press, New York, 1995, pp. 10–21). The dynamic change bug refers to errors introduced by migrating a case (i.e., a process instance) from the old process definition to the new one. A transfer from the old process to the new process can lead to duplication of work, skipping of tasks, deadlocks, and livelocks. This paper describes an approach for calculating a safe change region. If a case is in such a change region, the transfer is postponed.