In this paper, we present black burst synchronization (BBS), a novel protocol for decentralized network-wide tick synchronization in wireless ad hoc networks, located at MAC level. We argue that tick synchronization is sufficient for multi- hop medium slotting, and that it can be used as a basis for time synchronization. BBS is based on the exchange of synchronized tick frames, which are protected against collisions by a special encoding with black bursts. We deduce a deterministic bound for tick accuracy that depends linearly on maximum network diameter, clear channel assessment delay jitter, and transceiver switching time only. In an improved version of BBS, tick accuracy becomes independent of switching time. We show that BBS has low complexity in terms of communication, computation, storage, and energy consumption, provides a low and deterministic convergence delay, and is robust against node movements and node failures. We have implemented BBS on MICAz motes, and have experimentally validated its predicted behavior. In addition, we have simulated BBS to study its behavior in larger and denser networks.