The present invention relates to a proteinaceous construct (also designated as polymer-VWF-conjugate) comprising plasmatic and/or recombinant von Willebrand factor (VWF), said VWF being bound to at least one physiologically acceptable polymer molecule, as well as to a complex between said proteinaceous construct and at least one factor VIII (FVIII) protein. The physiologically acceptable polymer molecule can be, for instance, polyethylene glycol (PEG) or polysialic acid (PSA). Further the present invention relates to methods for prolonging the in vivo-half-life of VWF or FVIII in the blood of a mammal having a bleeding disorder associated with functional defects of or deficiencies of at least one of FVIII or VWF.