A gas turbine engine includes in axial flow series a fan rotor, a series of outlet guide vanes for guiding flow from the fan rotor; and a bifurcation. The gas turbine engine further includes a substantially annular fluid passageway extending from fan to the bifurcation, the outlet guide vanes being positioned within the passageway. The passageway includes a profiled region positioned upstream of the bifurcation, the profiled region including a first circumferential portion positioned adjacent a second circumferential portion, the first circumferential portion having a first average radial thickness and a second circumferential portion having a second average radial thickness, the first average radial thickness being smaller than second average radial thickness. The profiled region of the passageway is configured to modify the flow through the passageway so as to improve uniformity of a static pressure field from immediately upstream of the bifurcation to just downstream of the fan rotor.