diff --git a/include/boost/phoenix/stl/tuple.hpp b/include/boost/phoenix/stl/tuple.hpp
index a83014a..9d49487 100644
--- a/include/boost/phoenix/stl/tuple.hpp
+++ b/include/boost/phoenix/stl/tuple.hpp
@@ -110,7 +110,7 @@ namespace boost { namespace phoenix {
     namespace placeholders {
         #define BOOST_PP_LOCAL_LIMITS (1, BOOST_PHOENIX_ARG_LIMIT)
         #define BOOST_PP_LOCAL_MACRO(N)                                                \
-            auto uarg##N =                                                             \
+            const auto uarg##N =                                                             \
             boost::phoenix::get_<(N)-1>(boost::phoenix::placeholders::arg1);
         #include BOOST_PP_LOCAL_ITERATE()
     }