We work in synthetic algebraic geometry. It is an extension of homotopy type theory by three axioms, which can be interpreted in a higher version of the Zariski topos and therefore gives a novel approach to algebraic geometry where a Zariski sheaf of higher groupoids is represented simply as a type. In this context we give a proof of Châtelet’s result that a Severi-Brauer variety with a point is a projective space. We make crucial use of étale sheaves, which can be defined and worked with conveniently in this synthetic approach.