diff --git a/include/mapnik/placement_finder.hpp b/include/mapnik/placement_finder.hpp
index 5be68bcbd..fb7cd13be 100644
--- a/include/mapnik/placement_finder.hpp
+++ b/include/mapnik/placement_finder.hpp
@@ -82,12 +82,8 @@ public:
 
     inline placements_type const& get_results() { return placements_; }
 
-    /** Additional boxes to take into account when finding placement.
-     * Used for finding line placements where multiple placements are returned.
-     * Boxes are relative to starting point of current placement.
-     * Only used for point placements!
-     */
-    std::vector<box2d<double> > additional_boxes;
+    std::vector<box2d<double> > & additional_boxes() { return additional_boxes_;}
+    std::vector<box2d<double> > const& additional_boxes() const { return additional_boxes_;}
 
     void set_collect_extents(bool collect) { collect_extents_ = collect; }
     bool get_collect_extents() const { return collect_extents_; }
@@ -160,6 +156,13 @@ private:
     box2d<double> extents_;
     /** Collect a bounding box of all texts placed. */
     bool collect_extents_;
+
+    /** Additional boxes to take into account when finding placement.
+     * Used for finding line placements where multiple placements are returned.
+     * Boxes are relative to starting point of current placement.
+     * Only used for point placements!
+     */
+    std::vector<box2d<double> > additional_boxes_;
 };
 }
 
diff --git a/src/placement_finder.cpp b/src/placement_finder.cpp
index eefbf1b6e..f5a34b61e 100644
--- a/src/placement_finder.cpp
+++ b/src/placement_finder.cpp
@@ -500,9 +500,9 @@ void placement_finder<DetectorT>::find_point_placement(double label_x,
     }
 
     // check the placement of any additional envelopes
-    if (!p.allow_overlap && !additional_boxes.empty())
+    if (!p.allow_overlap && !additional_boxes_.empty())
     {
-        BOOST_FOREACH(box2d<double> box, additional_boxes)
+        BOOST_FOREACH(box2d<double> const& box, additional_boxes_)
         {
             box2d<double> pt(box.minx() + current_placement->center.x,
                              box.miny() + current_placement->center.y,
diff --git a/src/symbolizer_helpers.cpp b/src/symbolizer_helpers.cpp
index 03d584502..87516c19d 100644
--- a/src/symbolizer_helpers.cpp
+++ b/src/symbolizer_helpers.cpp
@@ -380,9 +380,9 @@ template <typename FaceManagerT, typename DetectorT>
 bool shield_symbolizer_helper<FaceManagerT, DetectorT>::next_line_placement()
 {
     position const& pos = placement_->properties.displacement;
-    finder_->additional_boxes.clear();
+    finder_->additional_boxes().clear();
     //Markers are automatically centered
-    finder_->additional_boxes.push_back(
+    finder_->additional_boxes().push_back(
         box2d<double>(-0.5 * marker_ext_.width()  - pos.first,
                       -0.5 * marker_ext_.height() - pos.second,
                       0.5 * marker_ext_.width()  - pos.first,