A hydraulic tensioner is provided with a no-return device and with an anti-rotation device capable of being disabled having a pin, integral with the cylinder of the tensioner, which slides in a first longitudinal slot formed on the outer wall of the piston and a means able to disable the anti-rotation device. The disabling means includes a second slot, at right angles with respect to the first longitudinal slot to which it is connected, situated at the end of the first longitudinal slot nearer to the bottom of the cylinder. The second slot may also be a throat connected to the first longitudinal slot to which it is perpendicular, and which extends for the whole circumference of the piston. The second slot is preferably shaped as a ramp to join the bottom of the first longitudinal slot to the outer surface of the piston.