Efficient spectrum usage and optimized energy consumption directly depend on the radio duty cycle of the communicating devices. Tight synchronization of communicating nodes enables optimal orchestration of the access to the medium as nodes turn their radios on precisely when needed. Achieving synchronization, however, requires a reference time source to synchronize with and a periodic discipline mechanism to cope with the inherent clock drift. Packet-based synchronization or external time sources, such as GPS, are usually required to achieve that goal. When low-power operation is combined with bandwidth limitations and scale, as in the case of low power wide area networks, the overhead of such approaches is not affordable and advanced clock discipline mechanisms are required. In this paper, we propose a novel adaptive mechanism to discipline clocks in order to guarantee a 1 ppm drift with minimal communication overhead.