We investigate experimental limitations in the accuracy of Fourier-transform spectral interferometry, a widely used technique for determining the spectral phase difference between two light beams consisting of, for example, femtosecond light pulses. We demonstrate that the spectrometer's finite spectral resolution, pixel aliasing, and frequency-interpolation error can play an important role, and we provide a new and more accurate recipe for recovering the spectral phase from the experimental data. Cop. 2000 Optical Society of America