A tensioner for the chain or the belt of an internal combustion engine, for example of the camshaft drive, includes a cylindrical tensioner housing (2) with a piston (1) loaded by a compression spring (13) arranged therein, the tensioner housing and the piston being axially displaceable relative to each other. The displaceable element which is displaceable relative to the fixed element in chain tensioning direction, is surrounded by a first stop ring which limits its backward movement. According to the invention, the first stop ring is configured as a retaining clip (15) whose arms engage into a locking groove (16) of the tensioner housing (2) under radial pre-stress and, upon a displacement thereof, can come to bear axially against a stop surface of the receiving housing (3).