The structure of one of the high-temperature polymorphs of Na2ZnSiO4 has been determined from powder diffractometer data, recorded at 750 degrees C with CuK alpha radiation. Differential scanning calorimetry showed that the reversible phase transition from the low-temperature modification occurs at ca. 600 degrees C, with an enthalpy of 1.45 kJ/mol. The high-temperature modification crystallises in space group Pna2(1) with a = 10.759(2), b = 5.313(1), c = 7.211(1) Angstrom and V = 412.2 Angstrom(3). The structure was refined by the Rietveld method to R(F) = 5.7%, using 285 reflections in the 2 theta range 15-110 degrees. The structural relationship between the low- and high-temperature modifications is discussed.