A movable pentaprism is a key element in deflectometric profilers, where it directs the beam of an angle measuring device towards the surface under test and enables at the same time the flexible lateral displacement of the beam footprint on the surface. The beam deflection angle of the pentaprism is robust with regard to changes in its angular orientation. Optimal stability is achieved, however, only when the angle measuring device, the pentaprism, and the surface have initially been properly aligned. A newly developed procedure enables the rapid and accurate in-situ adjustment of all angles of the optical components in deflectometric set-ups with an uncertainty of several microrad. In combination with precision mechanical stages, variations in the prism’s deflection angle (caused by changes in its angular orientation) can then be limited to the nanorad level.