The design of supervisory controllers to resolve any deadlock issue in automated manufacturing systems (AMSs) has attracted the efforts of many researchers. A great deal of work, which assumes that allocated resources do not fail, has been done, while only a few works pay attention to the existence of unreliable resources in AMSs. In this paper, we focus on the robust supervisory control for avoiding deadlocks in AMSs, each of which has one specified unreliable resource. We develop a robust supervisory control policy under which the system can continue producing without manual intervention in the face of the unreliable resource’s failure and recovery. Our policy consists of a modified Banker’s Algorithm and the available resource constraints. After proving the correctness of our policy, we show that there are more reachable states under our policy than the existing one. Therefore, our policy imposes less restrictive constraints on the system and is more permissive than the original one. Finally, an example is provided to illustrate our control policy’s advantage in permissiveness.