diff --git a/src/libraries/turtle/log.hpp b/src/libraries/turtle/log.hpp
index da136c2..0646ab2 100644
--- a/src/libraries/turtle/log.hpp
+++ b/src/libraries/turtle/log.hpp
@@ -116,7 +116,7 @@ namespace detail
         {}
     };
 
-    std::ostream& operator<<( std::ostream& s, const detail::sink& )
+    inline std::ostream& operator<<( std::ostream& s, const detail::sink& )
     {
         return s << "?";
     }