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We discuss SPaRe: selective partial replication, a methodology for concurrent fault detection in finite state machine (FSMs). The proposed method is similar to duplication, wherein a replica of the circuit acts as a predictor that immediately detects errors by comparison to the original FSM. However, instead of duplicating the FSM, SPaRe selects a few prediction functions which only partially replicate it. Selection is guided by the objective of minimizing the incurred hardware overhead without compromising the ability to detect all faults, yet possibly introducing fault-detection latency. SPaRe is nonintrusive and does not interfere with the encoding and implementation of the original FSM. Experimental results indicate that SPaRe achieves significant hardware overhead reduction over both duplication and test vector logic replication (TVLR), a previously reported concurrent fault-detection method. Moreover, as compared to TVLR, SPaRe also reduces the average fault-detection latency for detecting all permanent faults.