A rotor for a brushless permanent magnet generator/motor comprises a retention slot extending into a rotor flange for receiving a root of a permanent magnet. The retention slot comprises a base extending axially into the rotor flange, a pair of side walls extending radially from the base, and a pair of lugs projecting from the side wall to engage the root to provide radial and tangential retention of the permanent magnet. In other embodiments, the permanent magnet is further restrained in the axial direction by a spring pre-loaded axial retention ring.