An apparatus comprising: a functional circuit comprising one or more circuit components configured to perform a function based on one or more first input signals; at least one failure-prediction circuit for use in predicting failure of the functional circuit, the failure-prediction circuit comprising a replica of the functional circuit in terms of constituent circuit components; wherein the failure-prediction circuit is configured to be more susceptible to failure than said functional circuit, wherein the apparatus is configured to provide a prediction of failure of the functional circuit based on a determination of failure of the failure-prediction circuit.