A closure for a spout has a closure body having an annular body wall extending along a main axis between a closure base and an annular body wall edge. The closure is screwable to a spout having a connecting portion, suitable for welding to thin walls of a package, and a tube protruding from the connecting portion along a spout axis and ending with a mouth. The tube has a gripping section having a guide ring. Connection means connect the closure to the spout even when the closure is unscrewed. The connection means have a collar inserted on the gripping section of the spout and axially bound thereto by the guide ring, and an at least partially flexible tie that joins the collar to the closure.