Average QSO extinction curve of our sample compared with the Local Group extinction curves. The red shaded area illustrates the dispersion in the average QSO extinction curve. The extinction curves of the MW sightlines taken from Fitzpatrick & Massa (2007) are shown in grey. The SMC and LMC extinction curves taken from Gordon et al. (2003) are shown in charcoal dashed and dotted lines, respectively. The black solid line represents the extinction curve towards the MW star HD 210121. The black dashed line corresponds to the extinction curve towards the SMC AzV 23 sightline.