diff --git a/sd.go b/sd.go
index c421317..c3685e9 100644
--- a/sd.go
+++ b/sd.go
@@ -15,7 +15,6 @@ import (
 //sys lookupAccountSid(systemName *uint16, sid *byte, name *uint16, nameSize *uint32, refDomain *uint16, refDomainSize *uint32, sidNameUse *uint32) (err error) = advapi32.LookupAccountSidW
 //sys convertSidToStringSid(sid *byte, str **uint16) (err error) = advapi32.ConvertSidToStringSidW
 //sys convertStringSidToSid(str *uint16, sid **byte) (err error) = advapi32.ConvertStringSidToSidW
-//sys getSecurityDescriptorLength(sd uintptr) (len uint32) = advapi32.GetSecurityDescriptorLength
 
 type AccountLookupError struct {
 	Name string
@@ -121,7 +120,7 @@ func SddlToSecurityDescriptor(sddl string) ([]byte, error) {
 	if err != nil {
 		return nil, &SddlConversionError{Sddl: sddl, Err: err}
 	}
-	b := unsafe.Slice((*byte)(unsafe.Pointer(sd)), unsafe.Sizeof(windows.SECURITY_DESCRIPTOR{}))
+	b := unsafe.Slice((*byte)(unsafe.Pointer(sd)), sd.Length())
 	return b, nil
 }
 
diff --git a/zsyscall_windows.go b/zsyscall_windows.go
index 4923762..4e98e70 100644
--- a/zsyscall_windows.go
+++ b/zsyscall_windows.go
@@ -48,7 +48,6 @@ var (
 	procAdjustTokenPrivileges              = modadvapi32.NewProc("AdjustTokenPrivileges")
 	procConvertSidToStringSidW             = modadvapi32.NewProc("ConvertSidToStringSidW")
 	procConvertStringSidToSidW             = modadvapi32.NewProc("ConvertStringSidToSidW")
-	procGetSecurityDescriptorLength        = modadvapi32.NewProc("GetSecurityDescriptorLength")
 	procImpersonateSelf                    = modadvapi32.NewProc("ImpersonateSelf")
 	procLookupAccountNameW                 = modadvapi32.NewProc("LookupAccountNameW")
 	procLookupAccountSidW                  = modadvapi32.NewProc("LookupAccountSidW")
@@ -105,12 +104,6 @@ func convertStringSidToSid(str *uint16, sid **byte) (err error) {
 	return
 }
 
-func getSecurityDescriptorLength(sd uintptr) (len uint32) {
-	r0, _, _ := syscall.Syscall(procGetSecurityDescriptorLength.Addr(), 1, uintptr(sd), 0, 0)
-	len = uint32(r0)
-	return
-}
-
 func impersonateSelf(level uint32) (err error) {
 	r1, _, e1 := syscall.Syscall(procImpersonateSelf.Addr(), 1, uintptr(level), 0, 0)
 	if r1 == 0 {