A joint (1) having a first edge (2) and a second edge (3), the first edge (2) being provided with a distal edge (21) and a downwards protruding heel (22) The distal edge (21) is further provided with an upper joint edge (25) beneath which a groove (23) is arranged. The second edge (3) is provided with lower cheek (31) having a distal end (32) at which an upwards protruding lower cheek heel (33) is arranged. The second edge (3) is further provided with an upper joining edge (35) beneath which an undercut (34) is arranged. A moveable locking element (40) is arranged in the space created by the undercut (34). The moveable locking element (40) have a locking tongue (41), a locking tongue leg (42) and a maneuvering leg (43).