diff --git a/Boolean_set_operations_2/include/CGAL/Boolean_set_operations_2/Gps_agg_op.h b/Boolean_set_operations_2/include/CGAL/Boolean_set_operations_2/Gps_agg_op.h
index e0737433cec..6c2f54cc44c 100644
--- a/Boolean_set_operations_2/include/CGAL/Boolean_set_operations_2/Gps_agg_op.h
+++ b/Boolean_set_operations_2/include/CGAL/Boolean_set_operations_2/Gps_agg_op.h
@@ -38,7 +38,7 @@
 
 namespace CGAL {
 
-template <typename Arrangement_, typename BfsVisitor, template <typename, typename> class SweepVisitor>
+  template <typename Arrangement_, typename BfsVisitor, template <typename, typename, typename> class SweepVisitor>
 class Gps_agg_op {
   using Arrangement_2 = Arrangement_;
   using Bfs_visitor = BfsVisitor;