An analog-to-digital converter comprises a switched capacitor array configured to receive an analog input signal, a comparator having inputs coupled to respective outputs of the switched capacitor array, register circuitry having inputs coupled to respective outputs of the comparator, and a metastability detector associated with the register circuitry. The register circuitry is configured to generate control signals for application to respective control inputs of the switched capacitor array and to provide a digital output signal corresponding to the analog input signal. The metastability detector is configured to detect a metastability condition relating to signals at the respective outputs of the comparator. The register circuitry responsive to detection of the metastability condition forces bits of the digital output signal to particular logic levels. The register circuitry may comprise, for example, a successive approximation register, and the metastability detector may be at least partially incorporated within the successive approximation register.