diff --git a/include/mapnik/wkt/wkt_grammar_x3_def.hpp b/include/mapnik/wkt/wkt_grammar_x3_def.hpp
index f2cff7b21..2b6addcf4 100644
--- a/include/mapnik/wkt/wkt_grammar_x3_def.hpp
+++ b/include/mapnik/wkt/wkt_grammar_x3_def.hpp
@@ -27,19 +27,13 @@
 #include <mapnik/geometry/fusion_adapted.hpp>
 
 #if defined(__GNUC__)
-// instantiate `is_substitute` for const reference T and reference Attribute
+// instantiate `is_substitute` for reference T and reference Attribute
 // fixes gcc6 compilation issue
 namespace boost { namespace spirit { namespace x3 { namespace traits {
 
 template <typename T, typename Attribute, typename Enable>
 struct is_substitute<T&, Attribute&, Enable>
   : is_substitute<T, Attribute, Enable> {};
-
-//using ring_type = mapnik::geometry::linear_ring<double>;
-//template <>
-//struct is_substitute<ring_type const&, ring_type const& , void>
-//    : is_substitute<ring_type, ring_type, void>  {};
-
 }}}}
 #endif