diff --git a/relay32/user32.spec b/relay32/user32.spec
index 6d5316dcf7e..0a92baefac2 100644
--- a/relay32/user32.spec
+++ b/relay32/user32.spec
@@ -436,7 +436,7 @@ init	MAIN_UserInit
 432 stdcall RegisterClipboardFormatW(wstr) RegisterClipboardFormatW
 433 stdcall RegisterHotKey(long long long long) RegisterHotKey
 434 stdcall RegisterLogonProcess(long long) RegisterLogonProcess
-435 stub RegisterSystemThread
+435 stdcall RegisterSystemThread(long long) RegisterSystemThread
 436 stdcall RegisterTasklist (long) RegisterTaskList
 437 stdcall RegisterWindowMessageA(str) RegisterWindowMessageA
 438 stdcall RegisterWindowMessageW(wstr) RegisterWindowMessageW
diff --git a/windows/user.c b/windows/user.c
index 2bedecc94fb..5829db79a07 100644
--- a/windows/user.c
+++ b/windows/user.c
@@ -564,3 +564,11 @@ BOOL WINAPI SetSystemCursor(HCURSOR hcur, DWORD id)
 {	FIXME(win32,"(%08x,%08x),stub!\n",  hcur, id);
 	return TRUE;
 }
+
+/***********************************************************************
+ *	RegisterSystemThread	(USER32.435)
+ */
+void RegisterSystemThread(DWORD flags, DWORD reserved)
+{
+	FIXME(win32, "(%08lx, %08lx)\n", flags, reserved);
+}