diff --git a/src/enum.hpp b/src/enum.hpp
index 13695687..7df0b990 100644
--- a/src/enum.hpp
+++ b/src/enum.hpp
@@ -60,6 +60,7 @@ public:
     return _data;
   }
 
+  ENUM
   operator+() const
   {
     return _data;