Supervisory control in the context of w-languages is considered. The nominal supervisor design problem is to find a nonblocking supervisor for a nominal plant such that the closed-loop infinite behavior equals a specified closed-loop behavior. The robustness of solutions to the nominal problem is defined with respect to variations in the plant. It is shown there exists a supervisor solving the nominal problem which maximizes the set of plants for which the closed-loop languages for all other plants in the set satisfy loner and upper hounds in the sense of language containment. Computational issues are discussed, and the theoretical results are illustrated with an example.