diff --git a/toml/region.hpp b/toml/region.hpp
index bf9ba12..77ba943 100644
--- a/toml/region.hpp
+++ b/toml/region.hpp
@@ -511,7 +511,7 @@ inline std::string format_underline(const std::string& message,
         retval << '\n';
         retval << make_string(static_cast<std::size_t>(line_num_width + 1), ' ');
         retval << color::bold << color::blue << " | " << color::reset;
-        for(const auto help : helps)
+        for(const auto& help : helps)
         {
             retval << color::bold << "\nHint: " << color::reset;
             retval << help;
diff --git a/toml/serializer.hpp b/toml/serializer.hpp
index 6503f08..1a65d2b 100644
--- a/toml/serializer.hpp
+++ b/toml/serializer.hpp
@@ -619,7 +619,7 @@ struct serializer
 
         // print non-table stuff first. because after printing [foo.bar], the
         // remaining non-table values will be assigned into [foo.bar], not [foo]
-        for(const auto kv : v)
+        for(const auto& kv : v)
         {
             if(kv.second.is_table() || is_array_of_tables(kv.second))
             {