An integrated circuit for detecting harmonic lock of a phase-locked loop includes a frequency synthesizer for receiving a reference clock signal and for generating an oscillator clock signal. A phase generator receives the oscillator clock signal and generates a phase of the oscillator clock signal. A shift register receives as an input the reference clock signal and is clocked by the phase of the oscillator clock signal to produce an output that is a repetitive sequence of logic states. In an alternate embodiment, a harmonic decode circuit decodes the shift register output to determine which harmonic the phase-locked loop has locked onto.