Abstract: A disk stacker is provided with a wiping member which moves in timed relation to the disk. The wiping member can be an elongated flexible wiping member attached at one end to the shaft which rotates the disk, a second end of the wiping member being free to contact a sheet near the output position of the disk. Preferably, the wiping member has length sufficient to extend beyond the diameter of the disk to contact the uppermost sheet on the stack and re-register it against the front registration wall if it has bounced away therefrom. A retaining wall can be provided around a portion of the sheet so that the wiping member does not interfere with the inputting of sheets into the slots in the disk.