A variable-vane assembly for a variable nozzle turbine comprises a nozzle ring supporting a plurality of vanes affixed to vane arms that are engaged in recesses in the inner edge of a unison ring. The unison ring is rotatable about the axis of the nozzle ring so as to pivot the vane arms, thereby pivoting the vanes in unison. The unison ring is radially restrained by a combination of radial guide rollers and fixed axial-radial guide pins secured to the nozzle ring, and is axially restrained by one or more axial stops affixed to the nozzle ring.