Abstract: An improved latch bolt deadlocking mechanism includes a housing, a latch bolt, a deadlocking tumbler, and an auxiliary bolt. The latch bolt is movable along its longitudinal axis in the housing between projected and retracted positions. The deadlocking tumbler and the auxiliary bolt cooperate to selectively deadlock the latch bolt to retain the latch bolt in its projected position. The latch bolt is formed to include integral guides extending along the length of the latch bolt for guiding the auxiliary bolt along a straight path between a projected position holding the deadlocking tumbler in a release position to permit retraction of the latch bolt and a retracted position to permit movement of the deadlocking tumbler to its latch bolt-deadlocking position.