Simultaneous four optical light curves of a transit of WASP-174b obtained with GROND. Top panel: individual light-curves with arbitrary offsets for clarity. Bottom panel: all light-curves superimposed for comparison purposes. The passbands and their central wavelengths are labelled. Note how the transit light curve shape changes with wavelength. Contrary to higher-inclination transiting planetary systems, the transit in the g′ band is shallower than the other bands, because the transit is grazing and the limb darkening is stronger at bluer wavelengths. The same effect was observed in only another case, that is WASP-67b (Mancini et al. 2014).