Issues raised by Fillaux et al. [Chem. Phys. Lett., this issue] regarding the Letter by Wilson et al. [Chem. Phys. Lett. 381 (2003) 102] are considered, and the aims of the modelling undertaken by Wilson et al. on the potassium hydrogen maleate system reiterated, in particular the fact that the equilibrium PES is discussed in Wilson et al. (2003).