diff --git a/include/mapnik/expression_evaluator.hpp b/include/mapnik/expression_evaluator.hpp
index 1008be4ee..15c85c97b 100644
--- a/include/mapnik/expression_evaluator.hpp
+++ b/include/mapnik/expression_evaluator.hpp
@@ -47,9 +47,29 @@ struct evaluate : boost::static_visitor<T1>
     explicit evaluate(feature_type const& f)
         : feature_(f) {}
 
-    value_type operator() (value_type x) const
+    value_integer operator() (value_integer val) const
     {
-        return x;
+        return val;
+    }
+
+    value_double operator() (value_double val) const
+    {
+        return val;
+    }
+
+    value_bool operator() (value_bool val) const
+    {
+        return val;
+    }
+
+    value_null operator() (value_null val) const
+    {
+        return val;
+    }
+
+    value_unicode_string const& operator() (value_unicode_string const& str) const
+    {
+        return str;
     }
 
     value_type operator() (attribute const& attr) const
diff --git a/include/mapnik/expression_node_types.hpp b/include/mapnik/expression_node_types.hpp
index 6c1af39e6..53a998453 100644
--- a/include/mapnik/expression_node_types.hpp
+++ b/include/mapnik/expression_node_types.hpp
@@ -24,24 +24,17 @@
 #define MAPNIK_EXPRESSION_NODE_TYPES_HPP
 
 // mapnik
-//#include <mapnik/value.hpp>
-//#include <mapnik/attribute.hpp>
+#include <mapnik/value_types.hpp>
+#include <mapnik/value.hpp>
+#include <mapnik/attribute.hpp>
 
 // boost
-#include <boost/variant/variant_fwd.hpp>
-
-namespace boost { template <typename T> class recursive_wrapper; }
+#include <boost/mpl/vector/vector30.hpp>
+#include <boost/variant.hpp>
 
 namespace mapnik
 {
 
-struct attribute;
-struct geometry_type_attribute;
-namespace value_adl_barrier {
-  class value;
-}
-using value_adl_barrier::value;
-
 namespace tags  {
 struct negate
 {
@@ -174,8 +167,12 @@ struct regex_replace_node;
 
 typedef mapnik::value value_type;
 
-typedef boost::variant <
-value_type,
+typedef boost::mpl::vector24<
+value_null,
+value_bool,
+value_integer,
+value_double,
+value_unicode_string,
 attribute,
 geometry_type_attribute,
 boost::recursive_wrapper<unary_node<tags::negate> >,
@@ -195,7 +192,9 @@ boost::recursive_wrapper<binary_node<tags::logical_and> >,
 boost::recursive_wrapper<binary_node<tags::logical_or> >,
 boost::recursive_wrapper<regex_match_node>,
 boost::recursive_wrapper<regex_replace_node>
-> expr_node;
+>::type expr_types;
+
+typedef boost::make_recursive_variant_over<expr_types>::type expr_node;
 
 }