The present invention provides a device for shredding sheet material, comprising shredding means—(2) for shredding the sheet material and a feed conveyor system for feeding sheet material. The feed conveyor system comprises a suction duct (12) having an inlet (19) and an outlet (20), and suction means for sucking sheet material to be shredded from the feed location to the shredding means via the suction duct and for sucking sheet material shredded by the shredding means to the collecting location. The shredding means comprise at least one stationary shear blade (4) and at least one rotary shear blade (3), as well as drive means. The device further comprises detection means for detecting an increased risk of jamming of the shredding means during operation of the device, as well as blocking means (31) which operate in dependence on the detections made by the detection means for partially blocking the suction duct in a blocking position or releasing the suction duct in a free position.