In this paper, we address the problem of artificial boundary conditions for the symmetric linearized hyperbolic formulation of Einstein's equations introduced in [A.M. Alekseenko, D.N. Arnold, New first-order formulation for the Einstein equations, Phys. Rev. D (3) 68 (6) (2003) 064013, 6 pp.]. We prescribe simple boundary conditions that make the problem well-posed and preserve the constraints. (C) 2009 Elsevier Inc. All rights reserved.