diff --git a/libs/util/include/psemek/util/empty.hpp b/libs/util/include/psemek/util/empty.hpp
index bebfb2bd..dea05935 100644
--- a/libs/util/include/psemek/util/empty.hpp
+++ b/libs/util/include/psemek/util/empty.hpp
@@ -7,7 +7,7 @@ namespace psemek::util
 
 	struct empty{};
 
-	std::ostream & operator << (std::ostream & os, empty)
+	inline std::ostream & operator << (std::ostream & os, empty)
 	{
 		os << "empty";
 		return os;