The present invention provides a modified polypeptide which binds Factor VIII. The polypeptide comprises truncated von Willebrand Factor (VWF) which comprises a sequence as shown in SEQ ID NO:3 or a fragment thereof or a sequence 90% identical thereto, wherein the truncated VWF comprises at least one modification in comparison to SEQ ID NO: 3 in at least one position selected from the group consisting of SI, S3, LI 8, V42, S43, K149, N248, S279, V320, T325, Q395 and K418.