Abstract: A method for installing a closure in the mouth of a pre-made flexible bag. The closure may, for example, be a shrouded plastic zipper with or without a slider. The bag may, for example, have side gussets. In the disclosed embodiment, the bag is made using a laminated material comprising an interior layer of thermoplastic material and a non-interior layer of non-thermoplastic material, such as paper. The package is made by a method comprising the following steps: method for providing a bag with a closure, comprising the following steps: (a) slitting the bag along first and second lines so that a top marginal portion of one wall of the bag disposed between the first and second lines forms a flap; (b) folding back the flap to uncover a topmost portion of the other wall; (c) joining one side of a closure to at least a portion of the topmost portion of the other wall uncovered by step (b); and (d) joining a portion of the flap to the other side of the closure after steps (a)-(c) have been performed.