A fan outlet assembly comprises a fan discharge nozzle having a radially inner platform, a radially outer platform arranged coaxially and in radial alignment with the radially inner platform and a circumferential array of outlet guide vanes (110) spanning an annulus defined by the radially inner platform and radially outer platform. An annular duct extends downstream from the circumferential array, the duct having a radially outer wall (112) contiguous with the radially outer platform and a radially inner wall (111) contiguous with the radially inner platform. In a region extending downstream from the circumferential array, the radially inner and outer platforms and/or the radially inner and outer walls having a non-axisymmetric surface bounding the duct. A non-axisymmetric surface may be applied to either or both of the radially outer and radially inner contiguous surfaces and may extend upstream as well as downstream of the circumferential array of outlet guide vanes.