diff --git a/include/xo/reader/exprseq_xs.hpp b/include/xo/reader/exprseq_xs.hpp
index d6afffe8..1797855a 100644
--- a/include/xo/reader/exprseq_xs.hpp
+++ b/include/xo/reader/exprseq_xs.hpp
@@ -18,7 +18,7 @@ namespace xo {
         public:
             exprseq_xs();
 
-            static std::unique_ptr<exprseq_xs> expect_toplevel_expression_sequence();
+            static void start(exprstatestack * p_stack);
 
         public:
             // ----- token input methods -----
@@ -38,6 +38,8 @@ namespace xo {
                                  exprstatestack * p_stack,
                                  rp<Expression> * p_emit_expr) override;
 
+        private:
+            static std::unique_ptr<exprseq_xs> make();
         };
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/src/reader/exprseq_xs.cpp b/src/reader/exprseq_xs.cpp
index ed613dd2..840cd958 100644
--- a/src/reader/exprseq_xs.cpp
+++ b/src/reader/exprseq_xs.cpp
@@ -7,11 +7,17 @@
 namespace xo {
     namespace scm {
         std::unique_ptr<exprseq_xs>
-        exprseq_xs::expect_toplevel_expression_sequence()
+        exprseq_xs::make()
         {
             return std::make_unique<exprseq_xs>(exprseq_xs());
         }
 
+        void
+        exprseq_xs::start(exprstatestack * p_stack)
+        {
+            p_stack->push_exprstate(exprseq_xs::make());
+        }
+
         exprseq_xs::exprseq_xs()
             : exprstate(exprstatetype::expect_toplevel_expression_sequence)
         {
diff --git a/src/reader/parser.cpp b/src/reader/parser.cpp
index 5ac71dd0..5c2a99bb 100644
--- a/src/reader/parser.cpp
+++ b/src/reader/parser.cpp
@@ -30,8 +30,7 @@ namespace xo {
 
         void
         parser::begin_translation_unit() {
-            xs_stack_.push_exprstate
-                (exprseq_xs::expect_toplevel_expression_sequence());
+            exprseq_xs::start(&xs_stack_);
         }
 
         rp<Expression>