diff --git a/dix/window_priv.h b/dix/window_priv.h
index 874bc0f8c..cf28b1f70 100644
--- a/dix/window_priv.h
+++ b/dix/window_priv.h
@@ -31,5 +31,14 @@ WindowPtr dixCreateWindow(Window wid,
                           ClientPtr client,
                           VisualID visual,
                           int * error);
+/*
+ * @brief Make sure the window->optional structure exists.
+ *
+ * allocate if window->optional == NULL, otherwise do nothing.
+ *
+ * @param pWin the window to operate on
+ * @return FALSE if allocation failed, otherwise TRUE
+ */
+Bool MakeWindowOptional(WindowPtr pWin);
 
 #endif /* _XSERVER_DIX_WINDOW_PRIV_H */
diff --git a/include/window.h b/include/window.h
index ded5748cd..dffefbdcd 100644
--- a/include/window.h
+++ b/include/window.h
@@ -190,8 +190,6 @@ extern _X_EXPORT WindowPtr FindWindowWithOptional(WindowPtr /*w */ );
 
 extern _X_EXPORT void CheckWindowOptionalNeed(WindowPtr /*w */ );
 
-extern _X_EXPORT Bool MakeWindowOptional(WindowPtr /*pWin */ );
-
 extern _X_EXPORT WindowPtr MoveWindowInStack(WindowPtr /*pWin */ ,
                                              WindowPtr /*pNextSib */ );