A compressor bleed apparatus includes: a compressor comprising one or more rotors mounted for rotation about a central axis and enclosed in a compressor casing; a bleed slot passing through the compressor casing; an outer wall defining, in cooperation with the compressor casing, a plenum surrounding the compressor casing; at least one offtake pipe communicating with the plenum; and wherein at least one of the plenum and the bleed slot has a non-axisymmetric structure.