diff --git a/expression.hpp b/expression.hpp
index ab8b13e..d0d82be 100644
--- a/expression.hpp
+++ b/expression.hpp
@@ -141,9 +141,9 @@ namespace boost::proto17 {
     };
 
     template <typename T>
-    struct expression<expr_kind::terminal, T>
+    struct expression<expr_kind::terminal, hana::tuple<T>>
     {
-        using this_type = expression<expr_kind::terminal, T>;
+        using this_type = expression<expr_kind::terminal, hana::tuple<T>>;
         using tuple_type = hana::tuple<T>;
 
         static const expr_kind kind = expr_kind::terminal;
diff --git a/expression_fwd.hpp b/expression_fwd.hpp
index 0abfb30..3eb3da1 100644
--- a/expression_fwd.hpp
+++ b/expression_fwd.hpp
@@ -67,7 +67,7 @@ namespace boost::proto17 {
     struct expression;
 
     template <typename T, template <expr_kind, class> class expr_template = expression>
-    using terminal = expr_template<expr_kind::terminal, T>;
+    using terminal = expr_template<expr_kind::terminal, hana::tuple<T>>;
 
     template <typename T, template <expr_kind, class> class expr_template = expression>
     using expression_ref = expr_template<expr_kind::expr_ref, hana::tuple<std::remove_reference_t<T> *>>;