From 38876049c9f1164d2dab5b33d3932eee304dd939 Mon Sep 17 00:00:00 2001
From: molpopogen <krthornt@uci.edu>
Date: Wed, 7 Jul 2021 13:57:19 -0700
Subject: [PATCH] optional should wrap a reference_wrapper

---
 fwdpp/ts/types/tree_sequence.hpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fwdpp/ts/types/tree_sequence.hpp b/fwdpp/ts/types/tree_sequence.hpp
index 475fc9548..6eeebca71 100644
--- a/fwdpp/ts/types/tree_sequence.hpp
+++ b/fwdpp/ts/types/tree_sequence.hpp
@@ -43,11 +43,12 @@ namespace fwdpp
                 }
 
 #if __cplusplus >= 201703L
-                std::optional<const marginal_tree<SignedInteger>&>
+                std::optional<std::reference_wrapper<const marginal_tree<SignedInteger>>>
                 tree() const
                 {
                     // FIXME: should be nullopt if no more trees
-                    return std::optional<const marginal_tree<SignedInteger>&>{
+                    return std::optional<
+                        std::reference_wrapper<const marginal_tree<SignedInteger>>>{
                         std::cref(tree_)};
                 }
 #endif