A secure Integrated Circuit (IC) includes functional circuitry, and protection circuitry configured to protect the functional circuitry against fault-injection attacks. The protection circuitry includes a plurality of digital detection cells, and protection logic. The detection cells have respective inputs and outputs and are connected output-to-input in at least a chain. In response to a fault-injection attack, a given detection cell in the chain is configured to toggle an output that drives an input of a subsequent detection cell in the chain, thereby causing a pulse to propagate along the chain. The protection logic is configured to receive the pulse from the chain and initiate a responsive action.