Beckman and Quarles proved that a unit distance preserving mapping from a Euclidean space E into itself is necessarily an isometry. In this paper, we give an example of a (non-strictly convex) normed space H for which every unit distance preserving function from H into itself is an isometry. MSC 2000: 51M05, 52A10, 52A20, 52C05, 52C25