In a steam turbine, a combined brush and labyrinth seal is provided between a diaphragm web and a radially outwardly projecting platform between axially adjacent wheels on the rotor. The brush seal is located upstream of the labyrinth seal teeth. The platform has at least one and preferably a pair of flanges or fins projecting in opposite axial directions adjacent radial outer ends of the platform. Non-uniform heat distribution resulting from the frictional contact between the bristles of the brush seal and a sealing surface on the platform along the rotor surface affecting rotor dynamics is thereby eliminated or minimized.