diff --git a/include/mapnik/expression_evaluator.hpp b/include/mapnik/expression_evaluator.hpp
index b2155f9da..a4d199012 100644
--- a/include/mapnik/expression_evaluator.hpp
+++ b/include/mapnik/expression_evaluator.hpp
@@ -73,6 +73,12 @@ struct evaluate : boost::static_visitor<T1>
 
     template <typename Tag>
     value_type operator() (unary_node<Tag> const& x) const
+    {
+        typename make_op<Tag>::type func;
+        return func(boost::apply_visitor(*this, x.expr));
+    }
+
+    value_type operator() (unary_node<tags::logical_not> const& x) const
     {
         return ! (boost::apply_visitor(evaluate<feature_type,value_type>(feature_),x.expr).to_bool());
     }
diff --git a/include/mapnik/expression_grammar.hpp b/include/mapnik/expression_grammar.hpp
index c62b537cf..c74b70d47 100644
--- a/include/mapnik/expression_grammar.hpp
+++ b/include/mapnik/expression_grammar.hpp
@@ -198,21 +198,26 @@ struct expression_grammar : qi::grammar<Iterator, expr_node(), space_type>
                 | ( (lit('>')  | lit("gt") ) >> additive_expr [ _val >  _1 ])
                 )
             ;
+
         additive_expr = multiplicative_expr [_val = _1]
             >> * (   '+' >> multiplicative_expr[_val += _1]
                      | '-' >> multiplicative_expr[_val -= _1]
                 )
             ;
 
-        multiplicative_expr = primary_expr [_val = _1]
-            >> *(     '*' >> primary_expr [_val *= _1]
-                      | '/' >> primary_expr [_val /= _1]
-                      | '%' >> primary_expr [_val %= _1]
+        multiplicative_expr = unary_expr [_val = _1]
+            >> *(     '*' >> unary_expr [_val *= _1]
+                      | '/' >> unary_expr [_val /= _1]
+                      | '%' >> unary_expr [_val %= _1]
                       |  regex_match_expr[_val = regex_match_(_val, _1)]
                       |  regex_replace_expr(_val) [_val = _1]
                 )
             ;
 
+        unary_expr = primary_expr [_val = _1]
+            | '+' >> primary_expr [_val = _1]
+            | '-' >> primary_expr [_val = -_1]
+            ;
 
         primary_expr = strict_double [_val = _1]
             | int_ [_val = _1]
@@ -256,6 +261,7 @@ struct expression_grammar : qi::grammar<Iterator, expr_node(), space_type>
     rule_type logical_expr;
     rule_type additive_expr;
     rule_type multiplicative_expr;
+    rule_type unary_expr;
     rule_type not_expr;
     rule_type primary_expr;
     qi::rule<Iterator, std::string() > regex_match_expr;
diff --git a/include/mapnik/expression_node.hpp b/include/mapnik/expression_node.hpp
index 97608ec3b..a123297c5 100644
--- a/include/mapnik/expression_node.hpp
+++ b/include/mapnik/expression_node.hpp
@@ -40,6 +40,14 @@ namespace mapnik
 {
 
 namespace tags  {
+struct negate
+{
+    static const char* str()
+    {
+        return "-";
+    }
+};
+
 struct plus
 {
     static const char* str()
@@ -166,6 +174,7 @@ typedef mapnik::value value_type;
 typedef boost::variant <
 value_type,
 attribute,
+boost::recursive_wrapper<unary_node<tags::negate> >,
 boost::recursive_wrapper<binary_node<tags::plus> >,
 boost::recursive_wrapper<binary_node<tags::minus> >,
 boost::recursive_wrapper<binary_node<tags::mult> >,
@@ -185,6 +194,7 @@ boost::recursive_wrapper<regex_replace_node>
 > expr_node;
 
 template <typename Tag> struct make_op;
+template <> struct make_op<tags::negate> { typedef std::negate<value_type> type;};
 template <> struct make_op<tags::plus> { typedef std::plus<value_type> type;};
 template <> struct make_op<tags::minus> { typedef std::minus<value_type> type;};
 template <> struct make_op<tags::mult> { typedef std::multiplies<value_type> type;};
@@ -289,6 +299,11 @@ struct function_call
 
 // ops
 
+inline expr_node& operator- (expr_node& expr)
+{
+    return expr = unary_node<tags::negate>(expr);
+}
+
 inline expr_node & operator += ( expr_node &left ,const expr_node &right)
 {
     return left =  binary_node<tags::plus>(left,right);
diff --git a/include/mapnik/value.hpp b/include/mapnik/value.hpp
index ab892d63f..06b1bdc30 100644
--- a/include/mapnik/value.hpp
+++ b/include/mapnik/value.hpp
@@ -524,6 +524,29 @@ struct mod: public boost::static_visitor<V>
     }
 };
 
+template <typename V>
+struct negate : public boost::static_visitor<V>
+{
+    typedef V value_type;
+
+    template <typename T>
+    value_type operator() (T val) const
+    {
+        return -val;
+    }
+
+    value_type operator() (value_null const& val) const
+    {
+        return val;
+    }
+
+    value_type operator() (UnicodeString const& ustr) const
+    {
+        UnicodeString inplace(ustr);
+        return inplace.reverse();
+    }
+};
+
 struct to_bool : public boost::static_visitor<bool>
 {
     bool operator() (bool val) const
@@ -763,6 +786,11 @@ public:
         return boost::apply_visitor(impl::less_or_equal(),base_,other.base_);
     }
 
+    value operator- () const
+    {
+        return boost::apply_visitor(impl::negate<value>(), base_);
+    }
+
     value_base const& base() const
     {
         return base_;