A yarn brake includes a fixed frame, fixed and spaced-apart yarn guide elements defining together a straight yarn path through the yarn brake, a rotation drive, and at least one braking element projecting from the rotation drive beyond the straight yarn path. The braking element is controlled by the rotation drive to move through an angular stroke about a rotation axis that is spaced from and essentially parallel to the straight yarn path. The angular stroke has a starting position on one side of the path and a braking position on the other side of the path. An adjustment device varies the degree of deviation of the yarn by varying the braking position of the braking element. The distance between the rotation axis of the braking element and the straight yarn path is variable.