diff --git a/include/boost/none_t.hpp b/include/boost/none_t.hpp
index 008f369..9ed9409 100644
--- a/include/boost/none_t.hpp
+++ b/include/boost/none_t.hpp
@@ -29,7 +29,7 @@ class none_t {};
 struct none_t
 {
   struct init_tag{};
-  explicit none_t(init_tag){} // to disable default constructor
+  explicit constexpr none_t(init_tag){} // to disable default constructor
 };
 
 #endif // old implementation workarounds