The enthalpy of melting of NaMgF3 and KMgF3 at the dystectic temperature of fusion of these compounds was determined using a high-temperature calorimeter, the Setaram HTC 1800 K. It was found that Delta(fus)H(m)(NaMgF3; 1303 K) = (66+/-4) kJ mol(-1) and Delta(fus)H(m)(KMgF3; 1343 K) = (96+/-5) kJ mol(-1). The given error is calculated at the level of reliability (1 - alpha) = 0.95.