UpdateWindow returns a BOOLean.
diff --git a/include/winuser.h b/include/winuser.h
index a46355b..b2877d4 100644
--- a/include/winuser.h
+++ b/include/winuser.h
@@ -4441,7 +4441,7 @@
BOOL WINAPI UnregisterClassA(LPCSTR,HINSTANCE);
BOOL WINAPI UnregisterClassW(LPCWSTR,HINSTANCE);
#define UnregisterClass WINELIB_NAME_AW(UnregisterClass)
-VOID WINAPI UpdateWindow(HWND);
+BOOL WINAPI UpdateWindow(HWND);
UINT WINAPI UserRealizePalette(HDC);
BOOL WINAPI ValidateRect(HWND,const RECT*);
BOOL WINAPI ValidateRgn(HWND,HRGN);