diff --git a/include/mapnik/grid/grid_util.hpp b/include/mapnik/grid/grid_util.hpp
index f681debb7..b1b61c661 100644
--- a/include/mapnik/grid/grid_util.hpp
+++ b/include/mapnik/grid/grid_util.hpp
@@ -26,6 +26,9 @@
 // mapnik
 #include <mapnik/grid/grid.hpp>
 
+// boost
+#include <boost/concept_check.hpp>
+
 namespace mapnik {
 
 /*
@@ -57,6 +60,8 @@ static inline void scale_grid(mapnik::grid::data_type & target,
     unsigned yprt1 = 0;
     unsigned xprt = 0;
     unsigned xprt1 = 0;
+    boost::ignore_unused_variable_warning(yprt1);
+    boost::ignore_unused_variable_warning(xprt1);
 
     //no scaling or subpixel offset
     if (target_height == source_height && target_width == source_width && offs_x == 0 && offs_y == 0){