First epoch afterglow spectra with the flux of the host galaxy from the best-fit SED subtracted. Overplotted is the best-fit Fitzpatrick & Massa (2007) parametrization of the extinction curve with c₃ = 0 (no bump) shown by the red solid line. We assume an underlying power-law with slope set by a fit to the X-ray afterglow and assuming a Δβ = 0.5 cooling break between the X-rays and the optical. Regions affected by telluric absorption are removed from the fit. Also plotted is the extinction curve of the SMC as described by Gordon et al. (2003); blue dashed line) and with an decreased total-to-selective reddening, R_V (blue dotted line). These examples proves to show that the extinction can not simply be modelled by a standard or even steeper SMC-type reddening law. The parameters of the best-fit extinction curve diverges significantly from that known from the local analogs, most notable are the c₄ and c₅ values representing the far-UV curvature component, but also the flat value of R_V. These are required to model the extreme drop without assuming a bump in the extinction curve in combination with the otherwise blue spectrum.