Exchange-correlation functionals that depend on the non-interacting kinetic energy density (r) break gauge invariance in the presence of a magnetic field. This yields incorrect results for molecular magnetic properties. We propose a simple generalization of the kinetic energy density that resolves this problem. Our modification is validated by computing NMR absolute isotropic shielding constants and shielding anisotropies with c-dependent functionals for a representative set of molecules. The accuracy of tau-dependent approximations is found to surpass that of common generalized gradient approximations (GGA) and hybrid functionals for strongly deshielded nuclei. (C) 2004 Elsevier B.V. All rights reserved.