diff --git a/hw/xwin/win.h b/hw/xwin/win.h
index 74d3e89e0c..1f02bfa7b3 100644
--- a/hw/xwin/win.h
+++ b/hw/xwin/win.h
@@ -1396,7 +1396,7 @@ void
 winMWExtWMUpdateWindowDecoration (win32RootlessWindowPtr pRLWinPriv,
 				  winScreenInfoPtr pScreenInfo);
 
-BOOL CALLBACK
+wBOOL CALLBACK
 winMWExtWMDecorateWindow (HWND hwnd, LPARAM lParam);
 
 Bool
diff --git a/hw/xwin/winwin32rootlesswindow.c b/hw/xwin/winwin32rootlesswindow.c
index a08cb6820e..8c34343cee 100755
--- a/hw/xwin/winwin32rootlesswindow.c
+++ b/hw/xwin/winwin32rootlesswindow.c
@@ -188,7 +188,7 @@ winMWExtWMUpdateIcon (Window id)
  * winMWExtWMDecorateWindow - Update window style. Called by EnumWindows.
  */
 
-BOOL CALLBACK
+wBOOL CALLBACK
 winMWExtWMDecorateWindow (HWND hwnd, LPARAM lParam)
 {
   win32RootlessWindowPtr pRLWinPriv = NULL;