A combination door lock having a self-canceling combination mechanism which is secured inside the lock housing and is provided with spring-biased hook engaging fingers which engage one or more of the combination discs when these discs are aligned at a predetermined position where a retracting cam engages a bolt-retracting lever. Once the bolt is retracted by the lever these hook fingers engage with an associated combination disc and move it out of its predetermined position to a random position thereby scrambling or self-canceling the combination or the placement of the discs. Accordingly, it is not possible to predict the precise position of the combination discs after the bolt has been retracted and the door opened.