We find that the conjectured heterotic SO(32) five-brane sigma model develops
necessarily k-anomalies, and we investigate their form. We show that these
anomalies can be absorbed by modifications of the superspace constraints, that
satisfy automatically the modified Bianchi-identity dH7=X8 of N=1, D=10
supergravity. The k-anomalies induce in particular a quantum deformation of the
torsion constraint Tαβa=2γαβa.Comment: 15 pages, no figure