diff --git a/src/grid/grid_renderer.cpp b/src/grid/grid_renderer.cpp
index 73eccd109..861da92d3 100644
--- a/src/grid/grid_renderer.cpp
+++ b/src/grid/grid_renderer.cpp
@@ -62,10 +62,10 @@ grid_renderer<T>::grid_renderer(Map const& m, T & pixmap, double scale_factor, u
       width_(pixmap_.width()),
       height_(pixmap_.height()),
       scale_factor_(scale_factor),
-      t_(pixmap_.width(),pixmap_.width(),m.get_current_extent(),offset_x,offset_y),
+      t_(m.width(),m.height(),m.get_current_extent(),offset_x,offset_y),
       font_engine_(),
       font_manager_(font_engine_),
-      detector_(box2d<double>(-m.buffer_size(), -m.buffer_size(), pixmap_.width() + m.buffer_size(), pixmap_.height() + m.buffer_size())),
+      detector_(box2d<double>(-m.buffer_size(), -m.buffer_size(), m.width() + m.buffer_size() ,m.height() + m.buffer_size())),
       ras_ptr(new grid_rasterizer)
 {
 #ifdef MAPNIK_DEBUG