Assembly consisting of a reverse-flow combustion chamber for a turbomachine and a diffuser intended to be positioned at the outlet of a centrifugal compressor and comprising two faces running parallel to one another, the said combustion chamber comprising a first annular part configured to bear at least one injection system and a second annular part extending beyond this first part so as to form a guide canal for turning back the direction in which the gases passing through the chamber flow, with reference to the axis of rotation of the said turbomachine, the axis Y-Y of the said first part being secant with the said axis of rotation, the assembly being characterized in that the said faces of the diffuser have a curved shape which evolves parallel to that of the outer wall of the chamber at its turn-back canal.