Machine for folding a web in a zigzag manner

Machine for folding a web (3) in a zigzag manner to produce connected folded pages comprising a transport mechanism (2) for a web (3), a receiving device (5) at a bottom area of the machine for collecting the folded web, a folding mechanism (4) disposed between the transport mechanism (2) and the receiving device (5) and a detection means (19,20) to detect an improper fold disposed downstream from the folding mechanism (4) in the direction of forward web motion, means to move a web (3) backward in the folding mechanism (2) and a control device (22) connected to said means to move the web backward and the detection means (19,20), said control device arranged such that, at least upon the occurrence of a first detection of an improper fold by said detection means, the means for moving the web (3) backward in the folding mechanism (4) is actuated by said control device over such a distance that the improper fold is entirely unfolded and such that whereupon such unfolding the normal forward movement of the web (3) through the folding mechanism (4) is continued.