A belt brake is described for a safety belt for protecting occupants in a vehicle, which belt can be wound onto and unwound from a belt drum mounted rotationally about a belt shaft. A method for locking a safety belt is also described. The invention comprises at least one displaceable braking element for displacement along the belt shaft which is rotationally fixed to the belt shaft and is located between a first and a second thrust bearing. A first thrust bearing is forcibly guided along the belt shaft, thereby enabling the first thrust bearing to be transferred from a first position, in which the safety belt is wound on the belt drum with an axial distance a1 between the at least one braking element and the first thrust bearing, and to a second position, in which the safety belt is at least partially unwound from the belt drum with an axial distance a2 between the at least one braking element and the at least one thrust bearing where a2