Real-time collaborative editing systems allow a group of users to view and edit the same item at the same time from geographically dispersed sites. Consistency maintenance in the face of concurrent accesses to shared entities is one of the core issues in the design of these systems. The paper introduces a locking based approach that grid application developer environments can apply to protect the consistency properties of workflows during collaborative editing scenarios. We developed two pessimistic locking algorithms to assure that under no circumstances can application developers break the acyclic criteria of workflow graphs or add invalid edges to them. We prove that the algorithms result consistent graphs, moreover, do not result the cancellation of any user's editing transaction. We see that the second, improved algorithm gives much better performance in terms of number of concurrent users that can work on a graph.