The invention relates to a mixer (100) for a separate-stream nozzle of a turbojet, the mixer being designed to mix a hot inner stream from the combustion chamber of the turbojet with a cold outer stream from the fan of the turbojet. The mixer comprises an inner shroud (120) defining a flow channel for said hot inner stream, an outer shroud (110) disposed around the inner shroud (120) and co-operating therewith to define a flow channel for said cold outer stream, and a lobed structure (130) having lobes (1321, 1322) extending longitudinally from the trailing edges (110a, 120a) of said shrouds. The lobed structure (130) is made of a ceramic matrix composite material and is attached to the outer shroud (110) by flexible fastener tabs (140).