This paper deals with the effects of faults on circuits implemented with controllable-polarity transistors. We propose a new fault model that suits the characteristics of these devices, and report the results of a SPICE-based analysis of the effects of faults on the behavior of some basic gates implemented with them. Hence, we show that the considered devices are able to intrinsically tolerate a rather high number of faults. We finally exploit this property to build a robust and scalable adder which is shown to tolerate all single faults and more than 99.5% of the double faults. Its area, performance and leakage power characteristics are improved by 15%, 18% and 12%, respectively, when compared to an equivalent FinFET solution at 22-nm technology node.