  I show that the gravitational scattering amplitudes of a spin-5/2 field with
mass $m\ll M_{Pl}$ violate tree-level unitarity at energies
$\sqrt{s}\approx\sqrt{mM_{Pl}}$ if the coupling to gravity is minimal.
Unitarity up to energies $\sqrt{s}\approx M_{Pl}$ is restored by adding a
suitable non-minimal term, which gives rise to interactions violating the
(strong) equivalence principle. These interactions are only relevant at
distances $d\lequiv 1/m$.
