A horizontal shaft impact crusher, including a crusher housing having an inlet for material to be crushed and an outlet for material that has been crushed. An impeller is mounted on a horizontal shaft in the crusher housing and is operative for rotating around a horizontal axis. Material to be crushed is accelerated by the impeller against a curtain. An adjustment device is provided for adjusting the position of the curtain relative to the impeller. The crusher housing includes at least two guide rails to which the adjustment device is slidably connected. A retaining device is arranged to hold, with a predetermined holding force, the adjustment device in a crusher operation position relative to the guide rails. The adjustment device is movable along the guide rails from the crusher operation position and away from the impeller in response to an excessive force being transferred from the curtain to the adjustment device and exceeding the predetermined holding force.