The optimal layout of the fiber reinforcement to be placed on existing masonry structures is determined using topology optimization [1]. The problem can be conveniently formulated as the minimization of the amount of reinforcement required to keep tensile stresses in any masonry element below a prescribed threshold. Strength criteria for masonry elements are provided by means of a recently presented lower bound limit analysis homogenization model [2], relying into a discretization of one-fourth of the unit cell by six CST elements. The macroscopic strength domain of masonry can be obtained in closed form, thanks to the limited number of variables involved. A multi-constrained discrete formulation that locally controls the stress field over the whole design domain [3] is adopted. The contribution presents some preliminary numerical results addressing the fiber-reinforcement of a benchmark masonry wall.