Abstract: This invention relates to apparatus for infolding laterally protruding wings of a filled sack onto adhesive strips provided on the top of the sack. Said wings have been formed when the top end portion of the sack has been stretched flat and has been closed by a seam weld and has been folded down onto one half of the flattened top surface of the sack. Two folding bars or folding rods are movably mounted in a machine frame and protrude freely in the direction in which the sacks are conveyed. Said folding bars or rods are adapted to be lowered onto and raised from the top surface of each sack and have outer edges defining fold lines for the wings to be infolded. Holders are mounted in the machine frame on both sides of the sack standing upright on a support. Each of said holders carries a holder frame provided with a gripper arm for engaging one of the wings from below. An upper gripper arm for cooperating with the lower gripper arm is pivoted in each of said holder frames.