An electronic system comprising a system to be monitored (2) and a plurality of fault-monitoring systems (4, 6) each of which is adapted to output a fault signal when an input indicates that the electronic system is in a fault condition associated with the fault-monitoring system. The fault-monitoring systems are arranged in a cascade fashion such that a fault signal output from one fault-monitoring system (4) is provided as an input to a subsequent fault-monitoring system (6) in the cascade of fault-monitoring systems to simulate a fault condition associated with the subsequent fault-monitoring system. The output of the final fault-monitoring system in the cascade gives an indication of whether there is a fault with any of the fault-monitoring systems.