The invention relates to a rotor shaft (10) having a fastening section (12) along a fastening region of the shaft; and a plurality of permanent magnets (21, 22, 23, 24) which are fastened in the fastening section (12) to the rotor shaft (10), wherein the rotor shaft has a region in the fastening section having a reduced radius relative to a circular cross-section, so that a radially measured thickness of a permanent magnet (21) in the region is greater than in an adjacent region having a radius of the rotor shaft (10) which is not reduced.