Results of tests for deviations from linearity in GALEX detectors. A comparison is shown between "predicted" and measured magnitudes for a number of standard stars from the CALSPEC database (see text). "Predicted" values are magnitudes obtained through synthetic photometry on CALSPEC spectra by M07, while measured values are aperture magnitudes by M07 (curves) and PSF magnitudes from this work (data points). Gray (black) curves and open (filled) symbols represent NUV (FUV) magnitudes. Saturation becomes important at 14.5 mag for both channels alike, but is more intense in the FUV channel for brighter sources. Our PSF photometry seems to be only slightly more affected than M07's aperture photometry, in the FUV channel only. Only a handful of stars in our entire sample are substantially affected by detector nonlinearity.