Methods and apparatus are described for detecting anomalies in a clock signal. Example methods include sensing a clock signal that exhibits alternating phases during normal operation; responsive to sensing the start of a first phase, generating a pulse; and if the pulse terminates before sensing the end of the first phase, asserting a clock stopped detection signal. Example clock anomaly detection apparatus includes a clock signal input for coupling to a clock signal that, during normal operation, oscillates between first and second clock states. An anomaly detection output is asserted if the clock signal remains in the first clock state longer than a first phase expected duration or remains in the second clock state longer than a second phase expected duration.