Abstract: A snap locking device for a container with a cover which is lockable to the container via a bistable loosening flange. The flange is provided on the cover or the container and is adapted to cooperate with a locking edge on the container or the cover, respectively. The bistable loosening lines, and its portions disposded between at least two weakened lines are exteriorly provided with wall reinforcements which extend axially over the bistable loosening flange. The wall reinforcements preferably extend axially over the stationary cover flange disposed in extension of the loosening flange.