We consider, in five dimensions, the effective action from heterotic string which includes quantum gravity corrections up to (α ′ ) 2 . The expansion, in the string frame, is in terms of |α ′ R|, where R is the scalar curvature and uses the third order Euler density, next to the Gauss-Bonnet term. For a positive tension brane and infinite extra dimension, the logarithmic class of solutions is less dependent from fine-tuning than in previous formulations. More importantly, the model suggests that in the full non-perturbative formulation, the string scale can be much lower than the effective Planck mass, without the string coupling to be vanishingly small. Also, a less severe fine-tuning of the brane tension is needed.