A permanent magnet rotor comprising a rotor rim and a plurality of permanent magnet modules arranged on the outer or inner circumference of the rotor rim. The permanent magnet modules comprise a base adapted to be fixed to the rotor rim, one or more permanent magnets, and a central magnet support structure. The base and the central magnet support structure comprise a plurality of radial holes. The permanent magnet modules are adapted so that, when bolts are inserted in the radial holes to fix the central magnet support structure to the base, at least a portion of a first and a second surface of each permanent magnet remain substantially in conforming contact with a surface of the base and a surface of the central magnet support structure, respectively.