Soil water flux (J) can be estimated from the velocity (V) of a pulse of heat introduced into the soil. Here we consider a method in which V is measured with a three-probe sensor. The center probe heats the soil, and the outer probes measure temperature increases downstream (T d) and upstream (T u) from the heater. An equation was recently proposed for approximating J from the ratio T d/T u In this note we show that the accuracy of this equation can be improved by adding a term to correct for the time dependence of T d/T u This term is simple to evaluate and requires no additional measurements. Example calculations (three cases) are used to evaluate improvement in accuracy. When T d/T u is measured at a time of 45 s, relative errors in flux estimates are reduced from 10.5, 2.6, and −10.5% to 0.23, 0.06, and −0.23%, respectively, by using the correction term.