diff --git a/alib2std/src/extensions/set.hpp b/alib2std/src/extensions/set.hpp
index 06c908ac663cb91c07b8f4c80019c597ea40e795..3d1f639e96804979e2ed78fa6a383da08314cb4f 100644
--- a/alib2std/src/extensions/set.hpp
+++ b/alib2std/src/extensions/set.hpp
@@ -153,7 +153,14 @@ moveable_set<T> make_moveable_set (std::set<T>&& set) {
 	return moveable_set<T>(std::move(set));
 }
 
+template < class T >
+std::set < T > operator +( const std::set < T > & first, const std::set < T > & second ) {
+	std::set < T > res ( first );
+
+	res.insert ( second.begin ( ), second.end ( ) );
+	return res;
+}
+
 } /* namespace std */
 
 #endif /* __SET_HPP_ */
-