To the Gibbs function for seawater endorsed in 2008 by the International Association for the Properties of Water and Steam (IAPWS), an extension to higher temperature and salinity has been developed, based on density measurements at atmospheric pressure, temperatures up to 90 degrees C and absolute salinities up to 70 g/kg, as recently published by Millero and Huang (2009). In the range considered. the standard uncertainty in density of those data is less than 7 ppm. The new extension improves the applicability of the current standard formulation to hot seawater concentrates as encountered in desiccating seas or desalination plants, and maintains numerical consistency with most of the data used for the original formulation within their experimental uncertainties. Absolute salinity is expressed in the Reference-Composition Salinity Scale of 2008, temperature in the International Temperature Scale of 1990, ITS-90. (C) 2009 Elsevier B.V. All rights reserved.