A fortifying unit for fortifying opposite lateral walls of a storage unit, in particular of a cardboard box, in a fortified state, the fortifying unit comprising a fortifying shank, which comprises a first fortifying anchor, extends from the first fortifying anchor along a length to a free end and comprises at least one stop area between the first fortifying anchor and the free end, the stop area having a plurality of stop steps (61, 62, 63) disposed adjacent to each other along the length, the first fortifying anchor forming a first force-application surface in the fortified state for supporting one of the lateral walls (101, 103) from the outside, and a second fortifying anchor connectable to the fortifying shank and configured to support the opposite lateral wall (102, 104) by forming another force-application surface, the second fortifying anchor comprising stop means, which are formed in such a manner for interacting with the stop area that the second fortifying anchor is set in one of the fortifying steps for fortifying the lateral walls, the second fortifying anchor comprising an outer section having an outer contour fully closed in the circumferential direction and an inner section having an entry opening for inserting the free end and for guiding and/or positioning the stop area in the fortified state, characterized in that the entry opening for inserting the free end and for guiding and/or positioning the stop area has two sections (26, 27) in the fortified state, a first section with a larger cross section enabling the insertion of the free end and a second section with a smaller cross section allowing a positioning of the stop area in the fortified state. a fortifying shank, which comprises a first fortifying anchor, extends from the first fortifying anchor along a length to a free end and comprises at least one stop area between the first fortifying anchor and the free end, the stop area having a plurality of stop steps (61, 62, 63) disposed adjacent to each other along the length, the first fortifying anchor forming a first force-application surface in the fortified state for supporting one of the lateral walls (101, 103) from the outside, and a second fortifying anchor connectable to the fortifying shank and configured to support the opposite lateral wall (102, 104) by forming another force-application surface, the second fortifying anchor comprising stop means, which are formed in such a manner for interacting with the stop area that the second fortifying anchor is set in one of the fortifying steps for fortifying the lateral walls, the second fortifying anchor comprising an outer section having an outer contour fully closed in the circumferential direction and an inner section having an entry opening for inserting the free end and for guiding and/or positioning the stop area in the fortified state, characterized in that the entry opening for inserting the free end and for guiding and/or positioning the stop area has two sections (26, 27) in the fortified state, a first section with a larger cross section enabling the insertion of the free end and a second section with a smaller cross section allowing a positioning of the stop area in the fortified state.