The invention relates to a locking unit (4) for a seat belt retractor (1), which locking unit (4) is provided at one end of a seat belt spool (3) of the seat belt retractor (1), on which a seat belt (2) is retracted, so that when the seat belt (2) is quickly unrolled a locking arm (14) of a locking lever (13) is locked with an internal gearwheel (Z), as a result of which the seat belt spool (3) is locked, wherein the locking unit (4) has the following elements: the locking lever (13) with a center of rotation (D) arranged spaced apart from the center of the seat belt spool (3), an actuator arm (15) and the locking arm (14); a triggering unit having an inertia weight (17), a counter-pressure spring (18) and a transmission arm, which engages with the actuator arm (15), wherein the triggering unit is formed to rotate the locking lever (13) about the center of rotation (D) and to lock the locking arm (14) by means of the stationary internal gearwheel (Z) that is arranged about the locking lever (13) in the case of a fast acceleration of the unrolling of the safety belt (2), conditioned by the inertia force of the inertia weight (17) acting against the spring force of the counter-pressure spring (18), wherein a cover ring (19) is provided between the locking lever (13) and the internal gearwheel (Z), which cover ring (19) can be rotated into a covering position when the seat belt (2) is retracted, in which covering position the cover ring (19) at least partially covers the region between the locking arm (14) and the internal gearwheel (Z) in order to prevent locking, and which can be rotated into a release position when the seat belt (2) is unrolled, in which release position the cover ring (19) releases the region between the locking arm (14) and the internal gearwheel (Z) in order to permit locking.