A locking device for a carton comprising a first part and a second part complementary to the first part, the first part comprising a first panel (12) having an aperture for receiving the second part, the second part comprising a tab (22) coupled to a second panel, the tab having a fold line (15a, 15b) foldable to form a leading edge, the tab being inserted into the aperture in a folded condition, the tab comprising at least one engaging edge (30a, 30b) for engaging with the first panel.