A circuit includes an operation unit adapted to perform a circuit operation in a plurality of rounds. The operation unit may operate properly under a predetermined range of operating conditions. The operation unit is adapted to select between receiving an input signal and a test signal and to perform a test round of the circuit operation when the test signal is selected. The circuit is adapted to compare a reference value with a result of the test round, the reference value identifying a correct value for the result of the test round when the operation unit is operating under the predetermined range of operating conditions. The operation unit is further adapted to receive a disable signal to disable the operation unit from performing the circuit operation when the result of the test round does not match the reference value. Other embodiments are described and claimed.