Motivated by a nonlocal free boundary problem, we study uniform properties of solutions to a singular perturbation problem for a boundary-reaction-diffusion equation, where the reaction term is of combustion type. This boundary problem is related to the fractional Laplacian. After an optimal uniform Holder regularity is shown, we pass to the limit to study the free boundary problem it leads to. (C) 2015 Elsevier Ltd. All rights reserved.