diff --git a/tree/dataframe/inc/ROOT/RDFHelpers.hxx b/tree/dataframe/inc/ROOT/RDFHelpers.hxx
index 3ff582264a7b3890ac8df9ec7cc5445e68a09b13..12f72f67166d839831c77e8cc14c4b4532c9c919 100644
--- a/tree/dataframe/inc/ROOT/RDFHelpers.hxx
+++ b/tree/dataframe/inc/ROOT/RDFHelpers.hxx
@@ -35,7 +35,7 @@ std::function<bool(ArgTypes...)> NotHelper(ROOT::TypeTraits::TypeList<ArgTypes..
 }
 
 template <typename I, typename T, typename F>
-struct PassAsVecHelper;
+class PassAsVecHelper;
 
 template <std::size_t ... N, typename T, typename F>
 class PassAsVecHelper<std::index_sequence<N...>, T, F>