The cc-pVnZ/JKFit auxiliary basis sets of Weigend 4 are commonly used in DF-HF calculations with either the cc-pV(n+d)Z or cc-pVnZ-F12 orbital sets, but these auxiliary bases were not optimized for use with correlation consistent basis sets that include the additional tight-d functions. Werner and co-workers noted that this can lead to large errors, particularly when sulfur atoms are present. For example, using the aug-cc-pVTZ/JKFit auxiliary set in combination with F12 specific basis sets leads to a fitting error in the Hartree-Fock energy of 0.28 kcal mol -1 for the reaction C The addition of an ad hoc tight f-function and one g-function to the JKFit basis for sulfur reduced this error to 0.03 kcal mol -1 , and indicates that revising the JKFit basis sets to account for the tight-d function is important for high-accuracy calculations.