diff --git a/include/mapnik/value.hpp b/include/mapnik/value.hpp
index 8d986582f..c1604df73 100644
--- a/include/mapnik/value.hpp
+++ b/include/mapnik/value.hpp
@@ -182,22 +182,21 @@ struct not_equals
 
     bool operator() (value_null, value_null) const
     {
-        // TODO - needs review - https://github.com/mapnik/mapnik/issues/794
         return false;
     }
 
     template <typename T>
     bool operator() (value_null, const T &) const
     {
-        // TODO - needs review - https://github.com/mapnik/mapnik/issues/794
-        return false;
+        // https://github.com/mapnik/mapnik/issues/1642
+        return true;
     }
 
     template <typename T>
     bool operator() (const T &, value_null) const
     {
-        // TODO - needs review - https://github.com/mapnik/mapnik/issues/794
-        return false;
+        // https://github.com/mapnik/mapnik/issues/1642
+        return true;
     }
 };