D=10 supersymmetric Yang-Mills theory at alpha'^4

The ${\alpha }^{\mathrm{\prime }2}$ deformation of D=10 SYM is the natural generalisation of the $F^4$ term in the abelian Born-Infeld theory. It is shown that this deformation can be extended to ${\alpha }^{\mathrm{\prime }4}$ in a way which is consistent with supersymmetry. The latter requires the presence of higher-derivative and commutator terms as well as the symmetrised trace of the Born-Infeld ${\alpha }^{\mathrm{\prime }4}$ term.