A turbine for a turbo-machine is proposed in which, at a gas inlet for a turbine wheel, vanes extend from a nozzle ring though slots in a shroud. The nozzle ring and shroud are relatively rotatable about a rotational axis of the turbine by at least 0.1 degrees. In use, the nozzle ring and shroud are relatively rotated to bring one side of the vane into close contact with one surface of the slot, to inhibit leakage of gas between the vane and the slot surface. For this purpose the respective surfaces of the nozzle and slot can be configured to closely conform to each other. If there is differential thermal expansion of the shroud and nozzle ring, the nozzle ring and shroud can relatively rotate, to withdraw the vane from the edge of the slot to relieve the pressure between them.