diff --git a/dune/solvers/common/interval.hh b/dune/solvers/common/interval.hh
index 69524020ff0cdf9f43fc1b84016e84f13752aa17..f46d1599b880feb23392ef021d19ba30c9a29f7d 100644
--- a/dune/solvers/common/interval.hh
+++ b/dune/solvers/common/interval.hh
@@ -61,6 +61,9 @@ public:
      */
     field_type projectIn(const field_type& x) const
     {
+        // NB: C++17 has std::clamp(x, data_[0], data_[1]).
+        //     Note, however, that we need to guarantee neither
+        //     data_[0] nor data_[1] is NaN then.
         return std::max(std::min(x,data_[1]), data_[0]);
     }