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Fail-safe synchronous sequential machines produce safeside outputs when failures occur within the machine. This correspondence presents a procedure to design such machines using a modification of the on-set equation form originally presented by Tohma et al.  and later improved by Diaz et al. . A systematic procedure for state assignment and next-state equation derivation, using partition theory, is presented. From this method an easily calculated upper bound on the number of gates required-to realize a fail-safe circuit is derived.