This paper concerns the effect of symmetric supply voltage harmonics in a space-vector modulated three-phase indirect matrix converter (IMC). The IMC is controlled using indirect space-vector modulation. The effect of symmetric supply harmonics on load voltages and currents is analysed using space-vector presentation. The measurement and simulation results with distorted supply voltages are compared to the results with pure sinusoidal supply voltage. Three compensation methods are tested in simulations and measurements: 1) calculation of modulation index using measured supply voltages (method I), 2) feedback control of output currents (method II), and 3) combination of methods I and II, i.e. output current control with supply voltage measurement (method III). All methods are easy to implement and do not require complicated computing. It is noted that the methods I and III, where modulation index is calculated using measured supply voltages, compensate the effects of harmonics most effectively