diff --git a/plugins/input/postgis/postgis_datasource.cpp b/plugins/input/postgis/postgis_datasource.cpp
index c8d2fdef9..679a21861 100644
--- a/plugins/input/postgis/postgis_datasource.cpp
+++ b/plugins/input/postgis/postgis_datasource.cpp
@@ -502,15 +502,18 @@ featureset_ptr postgis_datasource::features(const query& q) const
             std::ostringstream s;
             s << "SELECT ST_AsBinary(\"" << geometryColumn_ << "\") AS geom";
 
+            mapnik::context_ptr ctx = boost::make_shared<mapnik::context_type>();
+
             if (!key_field_.empty())
+            {
                 mapnik::sql_utils::quote_attr(s,key_field_);
+                ctx->push(key_field_);
+            }
 
             std::set<std::string> const& props=q.property_names();
             std::set<std::string>::const_iterator pos=props.begin();
             std::set<std::string>::const_iterator end=props.end();
 
-            mapnik::context_ptr ctx = boost::make_shared<mapnik::context_type>();
-
             for ( ;pos != end;++pos)
             {
                 mapnik::sql_utils::quote_attr(s,*pos);
@@ -526,9 +529,6 @@ featureset_ptr postgis_datasource::features(const query& q) const
             }
 
             boost::shared_ptr<IResultSet> rs = get_resultset(conn, s.str());
-            unsigned num_attr = props.size();
-            if (!key_field_.empty())
-                ++num_attr;
             return boost::make_shared<postgis_featureset>(rs, ctx, desc_.get_encoding(), !key_field_.empty());
         }
         else
@@ -574,11 +574,14 @@ featureset_ptr postgis_datasource::features_at_point(coord2d const& pt) const
             std::ostringstream s;
             s << "SELECT ST_AsBinary(\"" << geometryColumn_ << "\") AS geom";
 
-            if (!key_field_.empty())
-                mapnik::sql_utils::quote_attr(s,key_field_);
-
             mapnik::context_ptr ctx = boost::make_shared<mapnik::context_type>();
 
+            if (!key_field_.empty())
+            {
+                mapnik::sql_utils::quote_attr(s,key_field_);
+                ctx->push(key_field_);
+            }
+
             std::vector<attribute_descriptor>::const_iterator itr = desc_.get_descriptors().begin();
             std::vector<attribute_descriptor>::const_iterator end = desc_.get_descriptors().end();