There is proposed a method and system for determining a phase-alignment between first and second clock signals of differing frequency. The method comprise: sampling a value of the first clock signal at instants defined by an edge of the second clock signal; defining a sequence of the sampled values of the first clock signal, wherein consecutive sample values in the sequence are separated by N cycles of the second clock signal, and wherein N is an integer greater than 1; and detecting the occurrence of a predetermined pattern of values in the defined sequence.