The shroud (26) of a shrouded turbine blade (22) has a convex leading edge (30) the apex of which extends towards the trailing edge of the shroud (24) of an adjacent, preceding guide vane. The extension enables the containment of a reverse flow of high pressure gas from the juncture of the blade aerofoil and shroud, until the pressure has dropped sufficiently to avoid nullifying gas flow from the corresponding portion of the guide vane (20) and thereby reduces excessive hot gas leakage from between the opposing shrouds edges.