A box for a flexible bag liner is formed from a blank of sheet material such as corrugated paperboard. The primary feature of the box is a retaining and locking structure for a spout of the bag liner disposed on an inner top flap. The inner top flap is attached to an inner portion of a side wall, and retains the spout in an aperture in either a retracted position or a dispensing position. The aperture secures the spout rigidly to facilitate filling and dispensing. An outer top flap covers the spout both during shipping and storage between uses.