A nut lock or locking cap secures a nut on a bolt so that the nut cannot loosen itself and so that the nut cannot fall off the bolt. For this purpose the nut lock has a first ring section that at least partially surrounds the bolt and a second ring section that at least partially surrounds the nut. The two ring sections are interconnected by a radially extending flange, whereby the first ring section has a smaller diameter than the diameter of the second ring section. The first ring section has at least one through-hole that can be aligned with a cross-bore in the bolt for the insertion of a locking pin. The second ring section has radially inwardly facing profiled surfaces that enter into a form-locking, force-transmitting connection with the outer profile of the nut.