Composition B is a melt-castable explosive consisting of RDX crystals in a TNT matrix. At elevated temperatures, the TNT can flow or even melt, which affects the particle distribution and therefore the detonation propagation. To study this phenomenon, rate stick experiments were conducted at ambient conditions, at temperatures below the TNT melt, and at temperatures above the TNT melt. We fielded shorting pins to measure the detonation velocity and a streak camera to record the detonation breakout. We report the measured velocities as a function of temperature and discuss the effect of temperature on detonation propagation. The need for temperature-dependent Composition B data in detonation shock dynamics simulations is discussed.