Negative lenses, either in the form of glasses or contact lenses, can correct nearsightedness. Unlike contact lenses, glasses do not only correct, but also induce optic distortions. In the scientific literature, it has often been assumed that people who wear corrective glasses instantaneously account for these distortions when they put their glasses on. We tested this assumption and found that, when people switched between their contact lenses and their glasses, they made the errors that one would predict based on the optics. This shows that people are not immediately adapted to their own glasses when they put them on.