An electric machine (101) for an aircraft is shown. The electric machine has a casing (104) containing electrical and electromechanical components, a shaft (106) which extends outside of the casing and which is connected to the propulsive fan, a seal (107) to seal the casing around the shaft, and a pressurization system (102) which pressurises the casing above an external pressure to prevent electrical breakdown within gas in the casing of the electric machine.