From 549b3d435351900efd3c3c37e5b7a0697e306e4e Mon Sep 17 00:00:00 2001
From: Jinhao <cnjinhao@hotmail.com>
Date: Thu, 7 Jun 2018 03:36:30 +0800
Subject: [PATCH] fix _nana_std_optional

---
 include/nana/optional.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/nana/optional.hpp b/include/nana/optional.hpp
index 1bb8373b..741e0b9f 100644
--- a/include/nana/optional.hpp
+++ b/include/nana/optional.hpp
@@ -17,7 +17,7 @@
 
 #include <nana/c++defines.hpp>
 
-#ifdef _nana_std_optional
+#ifndef _nana_std_optional
 #include <optional>
 #else
 #include <stdexcept>