A minor code update. An error concerning the calculation of solution viscosity, specific to mixtures involving aqueous CO2 as a species, has been resolved. We appreciate a related report from Hanyi Seok, bringing this issue to our attention. This minor bug-fix release includes a change to subroutine PureCompViscosity of module ModPureViscosPar to fix the CO2 issue. The remainder of the code is as for v3.12.