Perturbative unitarity for W_L⁺ W_L^- \to W_L⁺ W_L^- scattering is discussed within the Randall--Sundrum model. It is shown that the exchange of massive 4D Kaluza--Klein gravitons leads to amplitudes growing linearly with the CM energy squared. Summing over KK gravitons up to a scale \bar \Lambda  and testing unitarity at  \sqrt s=\bar \Lambda, one finds that unitarity is violated for  \bar \Lambda  below the ``naive dimensional analysis'' scale, \Lambda _NDA. It is also shown that the exchange of gravitons can substantially relax the upper limit from unitarity on the mass of the Standard Model Higgs boson --- consistency with unitarity for all \sqrt s below  \bar \Lambda  is possible for m_h as large as 1.4 TeV, depending on the curvature of the background metric. Observation of the mass and width (or cross section) of one or more KK gravitons at the LHC will directly determine the curvature and the scale  \Lambda _W  specifying the couplings of matter to the KK gravitons. With this information and a measurement of the Higgs boson mass it will be possible to determine the precise \sqrt s value below which unitarity will remain valid.

PACS numbers: 11.10.Kk, 04.50.+h, 11.15.--q, 11.80.Et