diff --git a/src/window_func.h b/src/window_func.h
--- a/src/window_func.h
+++ b/src/window_func.h
@@ -13,7 +13,6 @@ void SendWindowMessage(WindowClass wnd_c
 void SendWindowMessageClass(WindowClass wnd_class, int msg, int wparam, int lparam);
 
 Window *FindWindowById(WindowClass cls, WindowNumber number);
-void DeleteWindow(Window *w);
 void ChangeWindowOwner(PlayerID old_player, PlayerID new_player);
 
 void ResizeWindow(Window *w, int x, int y);