An apparatus for processing bank notes that includes an input unit for inputting bank notes, a singler for singling the input bank notes, a transport system for transporting the singled bank notes through a sensor device for checking the bank notes, a control device that evaluates signals from the sensor device, output units into which the bank notes are transported by the transport system, controlled by the control device, in dependence of the check, and detectors for monitoring the apparatus for the presence of malfunctions. The sensor device signals are evaluated by the control device for this purpose, and the control device stops the singler and the transport system in the event that the presence and/or the assumption of a malfunction is determined by the control device, wherein the control device, upon or after the stopping of the singler and of the transport system, effects an expansion of the transport system.