diff --git a/include/mapnik/unicode.hpp b/include/mapnik/unicode.hpp
index 092efb2e5..4522c3b8e 100644
--- a/include/mapnik/unicode.hpp
+++ b/include/mapnik/unicode.hpp
@@ -50,9 +50,12 @@ private:
 }
 
 namespace U_ICU_NAMESPACE {
-inline std::size_t hash_value(mapnik::value_unicode_string const& val) {
+
+inline std::size_t hash_value(mapnik::value_unicode_string const& val)
+{
     return val.hashCode();
 }
+
 }
 
 #endif // MAPNIK_UNICODE_HPP
diff --git a/include/mapnik/value.hpp b/include/mapnik/value.hpp
index 84470173e..647d0a295 100644
--- a/include/mapnik/value.hpp
+++ b/include/mapnik/value.hpp
@@ -25,6 +25,7 @@
 
 // mapnik
 #include <mapnik/value_types.hpp>
+#include <mapnik/value_hash.hpp>
 #include <mapnik/unicode.hpp>
 #include <mapnik/util/conversions.hpp>
 #include <mapnik/util/variant.hpp>
@@ -980,6 +981,12 @@ inline bool value::is_null() const
     return util::apply_visitor(mapnik::detail::is_null_visitor(), base_);
 }
 
+// hash function
+inline std::size_t hash_value(value const& val)
+{
+    return hash_value(val.base());
+}
+
 } // namespace mapnik
 
 #endif // MAPNIK_VALUE_HPP
diff --git a/include/mapnik/value_hash.hpp b/include/mapnik/value_hash.hpp
new file mode 100644
index 000000000..1137d9686
--- /dev/null
+++ b/include/mapnik/value_hash.hpp
@@ -0,0 +1,74 @@
+/*****************************************************************************
+ *
+ * This file is part of Mapnik (c++ mapping toolkit)
+ *
+ * Copyright (C) 2014 Artem Pavlenko
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ *****************************************************************************/
+
+#ifndef MAPNIK_VALUE_HASH_HPP
+#define MAPNIK_VALUE_HASH_HPP
+
+// mapnik
+#include <mapnik/util/variant.hpp>
+#include <mapnik/value_types.hpp>
+#include <mapnik/unicode.hpp>
+// stl
+#include <functional>
+
+namespace mapnik { namespace detail {
+
+template <class T>
+inline void hash_combine(std::size_t & seed, T const& v)
+{
+    std::hash<T> hasher;
+    seed ^= hasher(v) + 0x9e3779b9 + (seed<<6) + (seed>>2);
+}
+
+struct value_hasher: public util::static_visitor<std::size_t>
+{
+    std::size_t operator() (value_null val) const
+    {
+        return hash_value(val);
+    }
+
+    std::size_t operator() (value_unicode_string const& val) const
+    {
+        return hash_value(val);
+    }
+
+    template <class T>
+    std::size_t operator()(T const& val) const
+    {
+        std::hash<T> hasher;
+        return hasher(val);
+    }
+};
+
+} // namespace  detail
+
+template <typename T>
+std::size_t hash_value(T const& val)
+{
+    std::size_t seed = util::apply_visitor(detail::value_hasher(), val);
+    detail::hash_combine(seed, val.get_type_index());
+    return seed;
+}
+
+} // namespace mapnik
+
+#endif // MAPNIK_VALUE_HASH_HPP
diff --git a/include/mapnik/value_types.hpp b/include/mapnik/value_types.hpp
index 9b65b4c7a..58628ce0b 100644
--- a/include/mapnik/value_types.hpp
+++ b/include/mapnik/value_types.hpp
@@ -112,7 +112,8 @@ inline std::size_t hash_value(value_null const&)
 }
 
 template <typename TChar, typename TTraits>
-inline std::basic_ostream<TChar, TTraits>& operator<<(std::basic_ostream<TChar, TTraits>& out, value_null const& v) {
+inline std::basic_ostream<TChar, TTraits>& operator<<(std::basic_ostream<TChar, TTraits>& out, value_null const& v)
+{
     return out;
 }