Travelling wave harmonics of flux density on the rotor surface of a high-speed PM machine, caused by stator slotting, can produce substantial losses. A method is presented for calculating these losses, accounting for the true heteropolar nature of the problem. Harmonic waves are calculated by double FFT analysis of flux density data at the rotor surface, obtained from typically 60 magnetostatic solutions for different rotor positions. Electromagnetic losses for each harmonic are calculated using a 5-layer travelling current-sheet model. Results show that losses are strongly dependent on the sizes of airgap, magnet thickness, slot opening and slot pitch, and material properties.