Disclosed is a blood coagulation factor IX (FIX) with a FIX activation peptide region (AP region), wherein said AP region comprises a covalently coupled water-soluble hydrophilic polymer absent from biologically produced FIX, said covalently coupled water-soluble hydrophilic polymer being hydroxyethyl starch (HES) attached to said FIX via Asn-157 and/or Asn-167 of said FIX.