diff --git a/include/nana/gui/programming_interface.hpp b/include/nana/gui/programming_interface.hpp
index 4caef33e..b7e4a524 100644
--- a/include/nana/gui/programming_interface.hpp
+++ b/include/nana/gui/programming_interface.hpp
@@ -181,7 +181,7 @@ namespace API
 	template<typename Widget=::nana::widget, typename EnumFunction>
 	void enum_widgets(window wd, bool recursive, EnumFunction && fn)
 	{
-		static_assert(std::is_convertible<Widget, ::nana::widget>::value, "enum_widgets<Widget>: The specified Widget is not a widget type.");
+		static_assert(std::is_convertible<typename std::decay<Widget>::type*, ::nana::widget*>::value, "enum_widgets<Widget>: The specified Widget is not a widget type.");
 
 		detail::enum_widgets_function<Widget, EnumFunction> enum_fn(static_cast<EnumFunction&&>(fn));
 		enum_fn.enum_widgets(wd, recursive);
diff --git a/source/gui/filebox.cpp b/source/gui/filebox.cpp
index 2a690894..ae90915d 100644
--- a/source/gui/filebox.cpp
+++ b/source/gui/filebox.cpp
@@ -997,6 +997,9 @@ namespace nana
 
 			OPENFILENAME ofn;
 			memset(&ofn, 0, sizeof ofn);
+
+			internal_scope_guard lock;
+
 			ofn.lStructSize = sizeof(ofn);
 			ofn.hwndOwner = reinterpret_cast<HWND>(API::root(impl_->owner));
 			ofn.lpstrFile = &(wfile[0]);