diff --git a/GaudiAlg/include/GaudiAlg/FunctionalTool.h b/GaudiAlg/include/GaudiAlg/FunctionalTool.h
index 49200612f10f6487dcbc47131d9bd1bc317bbf63..9c3a8fb33d4606d2ab8678547ee6a13522a5bb4b 100644
--- a/GaudiAlg/include/GaudiAlg/FunctionalTool.h
+++ b/GaudiAlg/include/GaudiAlg/FunctionalTool.h
@@ -19,7 +19,7 @@ namespace Gaudi::Functional {
                                           Traits::use_<Tr, BaseClass_t<Base>>>;
 
     template <typename Signature, typename Traits>
-    struct ToolBinder;
+    class ToolBinder;
 
     template <typename IFace, typename... Args, typename Traits>
     class ToolBinder<Gaudi::Interface::Bind::Box<IFace>( Args const&... ), Traits>