diff --git a/win/rfb_win32/Security.cxx b/win/rfb_win32/Security.cxx
index b8887a9..95ef1d8 100644
--- a/win/rfb_win32/Security.cxx
+++ b/win/rfb_win32/Security.cxx
@@ -186,7 +186,7 @@
     throw rdr::SystemException("SetSecurityDescriptorDacl", GetLastError());
   DWORD sdSize = GetSecurityDescriptorLength(&absSD);
   SecurityDescriptorPtr sd(sdSize);
-  if (!MakeSelfRelativeSD(&absSD, sd, &sdSize))
+  if (!MakeSelfRelativeSD(&absSD, (PSECURITY_DESCRIPTOR)sd.ptr, &sdSize))
     throw rdr::SystemException("MakeSelfRelativeSD", GetLastError());
   return sd.takeSD();
 }