We construct a local on-shell invariant in D = 11 supergravity from the non
local four-point tree scattering amplitude. Its existence, together with ea
rlier arguments, implies nonrenormalizability of the theory at lowest possi
ble, two loop, level. This invariant, whose leading bosonic terms are exhib
ited, may also express the leading, "zero-slope," M-theory corrections to i
ts D = 11 supergravity limit.