diff --git a/include/mapnik/expression_evaluator.hpp b/include/mapnik/expression_evaluator.hpp
index 2c1ab1464..58b34486e 100644
--- a/include/mapnik/expression_evaluator.hpp
+++ b/include/mapnik/expression_evaluator.hpp
@@ -45,27 +45,27 @@ struct evaluate
         : feature_(f),
           vars_(v) {}
 
-    value_integer operator() (value_integer val) const
+    value_type operator() (value_integer val) const
     {
         return val;
     }
 
-    value_double operator() (value_double val) const
+    value_type operator() (value_double val) const
     {
         return val;
     }
 
-    value_bool operator() (value_bool val) const
+    value_type operator() (value_bool val) const
     {
         return val;
     }
 
-    value_null operator() (value_null val) const
+    value_type operator() (value_null val) const
     {
         return val;
     }
 
-    value_unicode_string const& operator() (value_unicode_string const& str) const
+    value_type operator() (value_unicode_string const& str) const
     {
         return str;
     }