At low energies ( approximately=20 MeV) the Johnson-Soper adiabatic model (1976) for deuteron break up is inaccurate when applied to transfer reaction calculations. The assumed degeneracy of the n-p centre-of-mass energy in all break-up configurations results in a lack of phase averaging and, in particular, an overestimation of the break-up component of the entrance channel wavefunction near the nuclear surface, of most importance to transfer reactions. This inadequacy of the break-up wavefunction is studied quantitatively and shown not to be significant for application of the adiabatic theory to the (d, p) reaction at 79 MeV incident deuteron energy.