diff --git a/source/gui/detail/window_manager.cpp b/source/gui/detail/window_manager.cpp
index e301ca5e..f5f56e71 100644
--- a/source/gui/detail/window_manager.cpp
+++ b/source/gui/detail/window_manager.cpp
@@ -1,7 +1,7 @@
 /*
  *	Window Manager Implementation
  *	Nana C++ Library(http://www.nanapro.org)
- *	Copyright(C) 2003-2016 Jinhao(cnjinhao@hotmail.com)
+ *	Copyright(C) 2003-2017 Jinhao(cnjinhao@hotmail.com)
  *
  *	Distributed under the Boost Software License, Version 1.0.
  *	(See accompanying file LICENSE_1_0.txt or copy at
@@ -1386,6 +1386,7 @@ namespace detail
 
 		void window_manager::remove_trash_handle(unsigned tid)
 		{
+			internal_scope_guard lock;
 			impl_->wd_register.delete_trash(tid);
 		}