Abstract: In a tightening device for a drive belt in an internal combustion engine, particularly for a toothed belt in the camshaft gear with a tension roller supported on a pivoting lever comprising a tension spring acting upon the pivoting lever in the direction of tension and a blocking device opposing the motion of the pivoting lever, whose blocking element changes its position as a function of the temperature, the blocking element formed as an end stop by the free end (17) of a preferably plate shaped stop body (18) whose other end (19) is held in a fixed housing (1) wherein the end stop in the operating state of the internal combustion engine is disposed at a distance from the adjacent support face of the pivoting lever. The tightening device with the thermally adjustable end stop avoids a tooth jump, particularly in the case of long belts.