  For hybrid inflationary potentials, we derive the tunneling rate from field
configurations along the flat direction towards the waterfall regime. This
process competes with the classically rolling evolution of the scalar fields
and needs to be strongly subdominant for phenomenologically viable models.
Tunneling may exclude models with a mass scale below 10^12 GeV, but can be
suppressed by small values of the coupling constants. We find that tunneling is
negligible for those models, which do not require fine tuning in order to
cancel radiative corrections, in particular for GUT-scale SUSY inflation. In
contrast, electroweak scale hybrid inflation is not viable, unless the
inflaton-waterfall field coupling is smaller than approximately 10^-11.
