2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/7364We present an updated phase-coherent timing solution for the young, energetic pulsar PSR B1509-58 for twenty years of data. Using a partially phase-coherent timing analysis, we show that the second frequency derivative is changing in time implying a third frequency derivative of (-9+/-1)x10^-32 s^(-4). This value is consistent with the simple power law model of pulsar rotation.2 pages. To appear in "Young Neutron Stars and Their Environments"(IAU Symposium 218, ASP Conference Proceedings), eds F. Camilo and B.M. GaenslerAstrophysicstext