A control scheme is presented for realizing state fault-tolerance of asynchronous sequential machines. An unobservable disturbance input can infiltrate into asynchronous machines and provoke unauthorized state transitions. The objective is to propose automatic state feedback controllers that detect penetration of the disturbance input and counteract state faults so as to return the controlled machine to its original state. A necessary and sufficient condition for the existence of such a controller is presented in a theoretical framework and an architecture of asynchronous triple modular redundancy is addressed as a case study.