A turbine stage of a turbine engine, the stage including a rotor wheel mounted inside a sectorized ring carried by an outer casing, the outer casing including at least a circumferential rim housed in an annular cavity to attach a downstream end of the ring sector. A bottom wall of the annular cavity of the ring sector remains radially spaced apart from the circumferential rim of the outer casing to provide a thermally insulating space between them and includes a radial positioning mechanism acting on the circumferential rim.