Supersymmetric non-abelian Born-Infeld revisited

We determine the non-abelian Born-Infeld action, including fermions, as it results from the four-point tree-level open superstring scattering amplitud es at order alpha'(2). We find that, after an appropriate field redefinitio n all terms at this order can be written as a symmetrised trace. We confron t this action with the results that follow from kappa-symmetry and conclude that the recently proposed non-abelian kappa-symmetry cannot be extended t o cubic orders in the Born-Infeld curvature.