diff --git a/include/mapnik/group/group_layout_manager.hpp b/include/mapnik/group/group_layout_manager.hpp
index 3db329df8..b44921b93 100644
--- a/include/mapnik/group/group_layout_manager.hpp
+++ b/include/mapnik/group/group_layout_manager.hpp
@@ -40,7 +40,7 @@ using bound_box = box2d<double>;
 
 struct group_layout_manager
 {
-    group_layout_manager(const group_layout &layout)
+    group_layout_manager(group_layout const& layout)
         : layout_(layout),
           input_origin_(0, 0),
           member_boxes_(vector<bound_box>()),
@@ -49,7 +49,7 @@ struct group_layout_manager
     {
     }
 
-    group_layout_manager(const group_layout &layout, const pixel_position &input_origin)
+    group_layout_manager(group_layout const& layout, pixel_position const& input_origin)
         : layout_(layout),
           input_origin_(input_origin),
           member_boxes_(vector<bound_box>()),
@@ -58,8 +58,8 @@ struct group_layout_manager
     {
     }
 
-    group_layout_manager(const group_layout &layout, const pixel_position &input_origin,
-                         const vector<bound_box> &item_boxes)
+    group_layout_manager(group_layout const& layout, pixel_position const& input_origin,
+                         vector<bound_box> const& item_boxes)
         : layout_(layout),
           input_origin_(input_origin),
           member_boxes_(item_boxes),
@@ -68,19 +68,19 @@ struct group_layout_manager
     {
     }
 
-    inline void set_layout(const group_layout &layout)
+    inline void set_layout(group_layout const& layout)
     {
         layout_ = layout;
         update_layout_ = true;
     }
 
-    inline void add_member_bound_box(const bound_box &member_box)
+    inline void add_member_bound_box(bound_box const& member_box)
     {
         member_boxes_.push_back(member_box);
         update_layout_ = true;
     }
 
-    inline const pixel_position &offset_at(size_t i)
+    inline pixel_position const& offset_at(size_t i)
     {
         handle_update();
         return member_offsets_.at(i);
diff --git a/src/group/group_layout_manager.cpp b/src/group/group_layout_manager.cpp
index 6090d734f..7799d5fda 100644
--- a/src/group/group_layout_manager.cpp
+++ b/src/group/group_layout_manager.cpp
@@ -44,9 +44,9 @@ struct process_layout : public util::static_visitor<>
     //      and the offset values should position them around (0,0)
     pixel_position const& input_origin_;
 
-    process_layout(const vector<bound_box> &member_bboxes,
+    process_layout(vector<bound_box> const& member_bboxes,
                    vector<pixel_position> &member_offsets,
-                   const pixel_position &input_origin)
+                   pixel_position const& input_origin)
        : member_boxes_(member_bboxes),
          member_offsets_(member_offsets),
          input_origin_(input_origin)
@@ -140,7 +140,7 @@ private:
     // stores corresponding offset, and returns modified bounding box
     bound_box box_offset_align(size_t i, double x, double y, int x_dir, int y_dir) const
     {
-        const bound_box &box = member_boxes_[i];
+        bound_box const& box = member_boxes_[i];
         pixel_position offset((x_dir == 0 ? x - input_origin_.x : x - (x_dir < 0 ? box.maxx() : box.minx())),
                              (y_dir == 0 ? y - input_origin_.y : y - (y_dir < 0 ? box.maxy() : box.miny())));
 
@@ -152,8 +152,8 @@ private:
 bound_box group_layout_manager::offset_box_at(size_t i)
 {
     handle_update();
-    const pixel_position &offset = member_offsets_.at(i);
-    const bound_box &box = member_boxes_.at(i);
+    pixel_position const& offset = member_offsets_.at(i);
+    bound_box const& box = member_boxes_.at(i);
     return box2d<double>(box.minx() + offset.x, box.miny() + offset.y,
                          box.maxx() + offset.x, box.maxy() + offset.y);
 }