The invention describes a machine for printing material webs (4), which comprises a station (1, 11, 41) for monitoring the printed material web (4), with the station (1, 11, 41) for monitoring the material web (4) comprising a sensor (3, 13) for monitoring the web (4) and at least one counter support (2, 12) for guiding the web (4), with at least one counter support (2, 12) being located on the side of the web (4) facing away from the sensor (3, 13).The invention is characterized by a device for providing blow air, which shows jets (6, 7) extruding blow air in the area of the station (1, 11, 41) for monitoring the material web (4) at the side of the material web (4) facing the sensor (3, 13).