Correct fix so still runs under 2.7
Correct fix so still runs under 2.7

pabigot/pyxb,jonfoster/pyxb1,pabigot/pyxb,jonfoster/pyxb-upstream-mirror,CantemoInternal/pyxb,balanced/PyXB,balanced/PyXB,jonfoster/pyxb2,jonfoster/pyxb-upstream-mirror,jonfoster/pyxb1,CantemoInternal/pyxb,jonfoster/pyxb2,CantemoInternal/pyxb,jonfoster/pyxb2,jonfoster/pyxb-upstream-mirror,balanced/PyXB