A muffler comprising an inner wall and an outer wall, and comprising at least one sensor port, the sensor port comprising a boss suitable for receiving a sensor, wherein the boss is fixed to the inner wall, and wherein the outer wall is provided with an opening around the boss, characterised in that the muffler further comprises a sealing assembly comprising: - one or more cover plates (20,21) comprising at least an outer cover plate attached to the outer wall and provided with an opening that overlaps the opening around the boss and - at least one washer-type element that comprises a planar portion provided with an aperture and a tube portion protruding from the edge of the aperture, and wherein: - the planar portion of the washer-type element is mounted between the muffler and the outer cover plate, in a way that allows movement of the washer-type element relative to the outer cover plate in a direction parallel to said cover plate, - the tube portion of the washer-type element protrudes through the opening of the outer cover plate or through the opening in the outer wall of the muffler, - the tube portion of the washer-type element is fitted around the boss in such a way that: ∘ the boss is movable relative to the tube portion in a direction perpendicular to the planar portion of the washer-type element, ∘ when the boss moves in a direction parallel to the outer wall, and relative to said outer wall, the tube portion and thereby the washer-type element as a whole undergoes the same movement, relative to the outer wall and relative to the cover plate, - the dimensions of the planar portion of the washer-type element are such that the gap between the boss and the opening in the outer wall is closed off by said planar portion and by the one or more cover plates (20,21), regardless of the position of the boss relative to the outer wall. characterised in that the muffler further comprises a sealing assembly comprising: - one or more cover plates (20,21) comprising at least an outer cover plate attached to the outer wall and provided with an opening that overlaps the opening around the boss and - at least one washer-type element that comprises a planar portion provided with an aperture and a tube portion protruding from the edge of the aperture, - one or more cover plates (20,21) comprising at least an outer cover plate attached to the outer wall and provided with an opening that overlaps the opening around the boss and - at least one washer-type element that comprises a planar portion provided with an aperture and a tube portion protruding from the edge of the aperture, and wherein: - the planar portion of the washer-type element is mounted between the muffler and the outer cover plate, in a way that allows movement of the washer-type element relative to the outer cover plate in a direction parallel to said cover plate, - the tube portion of the washer-type element protrudes through the opening of the outer cover plate or through the opening in the outer wall of the muffler, - the tube portion of the washer-type element is fitted around the boss in such a way that: ∘ the boss is movable relative to the tube portion in a direction perpendicular to the planar portion of the washer-type element, ∘ when the boss moves in a direction parallel to the outer wall, and relative to said outer wall, the tube portion and thereby the washer-type element as a whole undergoes the same movement, relative to the outer wall and relative to the cover plate, - the dimensions of the planar portion of the washer-type element are such that the gap between the boss and the opening in the outer wall is closed off by said planar portion and by the one or more cover plates (20,21), regardless of the position of the boss relative to the outer wall. - the planar portion of the washer-type element is mounted between the muffler and the outer cover plate, in a way that allows movement of the washer-type element relative to the outer cover plate in a direction parallel to said cover plate, - the tube portion of the washer-type element protrudes through the opening of the outer cover plate or through the opening in the outer wall of the muffler, - the tube portion of the washer-type element is fitted around the boss in such a way that: ∘ the boss is movable relative to the tube portion in a direction perpendicular to the planar portion of the washer-type element, ∘ when the boss moves in a direction parallel to the outer wall, and relative to said outer wall, the tube portion and thereby the washer-type element as a whole undergoes the same movement, relative to the outer wall and relative to the cover plate, ∘ the boss is movable relative to the tube portion in a direction perpendicular to the planar portion of the washer-type element, ∘ when the boss moves in a direction parallel to the outer wall, and relative to said outer wall, the tube portion and thereby the washer-type element as a whole undergoes the same movement, relative to the outer wall and relative to the cover plate, - the dimensions of the planar portion of the washer-type element are such that the gap between the boss and the opening in the outer wall is closed off by said planar portion and by the one or more cover plates (20,21), regardless of the position of the boss relative to the outer wall.