A muffler for an exhaust gas system of an internal-combustion engine has an exhaust gas inlet and a first flow pipe arranged inside the muffler and completely penetrating the muffler. A shut-off device is arranged in the first flow pipe, for the shutting-off and opening-up an exhaust gas tail pipe which is situated downstream of the muffler and is connected with the first flow pipe. A second flow pipe partially penetrates the muffler, and has an overflow path between the first and second flow pipes situated inside the muffler. The first and the second flow pipes are connected with the exhaust gas inlet by way of a branching element and the shut-off device is arranged upstream of the muffler in the first flow pipe.