The accuracy of phase shifting interferometry is limited by reference phase errors caused by nonlinearities in the phase shifter movements, calibration errors of this device, phase drifts during the measuring interval, and low frequency mechanical vibrations. Since the error depends on the phase to be measured in a sinusoidal fashion one can greatly reduce its influence on the measuring results. For this purpose a function also containing the characteristic error function, is fitted to the measured data. In a second step the error function is subtracted from the measured phase values. In most cases an error reduction by 1 order of magnitude seems achievable as has been demonstrated by computer simulations.