The present disclosure provides a tank, in particular a plastic fuel tank, having a stiffening device, which penetrates the interior of the tank between opposite first and second wall parts of the tank and couples the wall parts to each other, whereby the tank can be subjected to increased interior pressure without damage. According to the present disclosure, the stiffening device comprises a first stiffening element, arranged on the first wall part, and a second stiffening element, arranged on the second wall part, wherein the first and second stiffening element have interacting coupling parts and wherein the first and second stiffening element can be connected to the first stiffening element with high tensile strength and, in the connected states, seals an opening in the second wall part by means of a flange cover.