  We extend the notion of the Higuchi bound and partial masslessness to
ghost-free nonlinear bimetric theories. This can be achieved in a simple way by
first considering linear massive spin-2 perturbations around maximally
symmetric background solutions, for which the linear gauge symmetry at the
Higuchi bound is easily identified. Then, requiring consistency between an
appropriate subset of these transformations and the dynamical nature of the
backgrounds, fixes all but one parameter in the bimetric interaction potential.
This specifies the theory up to the value of the Fierz-Pauli mass and leads to
the unique candidate for nonlinear partially massless bimetric theory.
