  We propose a mechanism to evade the Lyth bound in models of inflation. We
minimally extend the conventional single-field inflation model in general
relativity (GR) to a theory with non-vanishing graviton mass in the very early
universe. The modification primarily affects the tensor perturbation, while the
scalar and vector perturbations are the same as the ones in GR with a single
scalar field at least at the level of linear perturbation theory. During the
reheating stage, the graviton mass oscillates coherently and leads to resonant
amplification of the primordial tensor perturbation. After reheating the
graviton mass vanishes and we recover GR.
