The arrangement has an ion current detector (14,16,20), which forms an ion current path with the secondary side of the ignition coil and the ignition plug for applying a voltage to the plug to detect an ion current resulting from ions generated in the cylinder during combustion. A high pass filter removes the low frequency component of the ion current detector output signal. A signal masking device masks the output of the filter during a period in which LC resonance noise might result from the inductance of the secondary side of the ignition coil and the stray capacitance in the ion current path. A bandpass filter extracts a knock frequency component from the mask output signal and a knock detection device determines the presence or absence of knock from the bandpass filter output
