diff --git a/dlls/ntdll/ntdll.spec b/dlls/ntdll/ntdll.spec
index 9c0c595426a..e65bd364578 100644
--- a/dlls/ntdll/ntdll.spec
+++ b/dlls/ntdll/ntdll.spec
@@ -300,7 +300,7 @@ type	win32
 @ stub RtlConvertExclusiveToShared
 @ stub RtlConvertLongToLargeInteger
 @ stub RtlConvertSharedToExclusive
-@ stub RtlConvertSidToUnicodeString
+@ stdcall RtlConvertSidToUnicodeString(ptr ptr)RtlConvertSidToUnicodeString
 @ stub RtlConvertUiListToApiList
 @ stub RtlConvertUlongToLargeInteger
 @ stub RtlCopyLuid
diff --git a/dlls/ntdll/sec.c b/dlls/ntdll/sec.c
index 49707d74548..7a2e760c772 100644
--- a/dlls/ntdll/sec.c
+++ b/dlls/ntdll/sec.c
@@ -23,6 +23,7 @@
 
 #include "ntddk.h"
 #include "winreg.h"
+#include "ntdll_misc.h"
 
 DEFAULT_DEBUG_CHANNEL(ntdll);
 
@@ -693,3 +694,24 @@ NTSTATUS WINAPI RtlGetControlSecurityDescriptor(
 	FIXME("(%p,%p,%p),stub!\n",pSecurityDescriptor,pControl,lpdwRevision);
 	return STATUS_SUCCESS;
 }		
+
+/******************************************************************************
+ * RtlConvertSidToUnicodeString
+ */
+NTSTATUS WINAPI RtlConvertSidToUnicodeString(
+       PUNICODE_STRING UnicodeSID,
+       PSID *pSid)
+{
+/*	LPSTR GenSID = "S-1-5-21-0000000000-000000000-0000000000-500"; */
+
+	LPSTR GenSID = ".Default";	/* usually the returned SID is used to */
+					/* access  "\\REGISTRY\\USER\\.DEFAULT" */
+
+        ANSI_STRING AnsiStr;
+
+	FIXME("(%p %p)\n", UnicodeSID, pSid);
+	dump_UnicodeString(UnicodeSID, FALSE);
+
+        RtlInitAnsiString(&AnsiStr, GenSID);
+        return RtlAnsiStringToUnicodeString(UnicodeSID, &AnsiStr, TRUE);
+}