diff --git a/include/mapnik/grid/grid_util.hpp b/include/mapnik/grid/grid_util.hpp
index 8a48f11b0..2ea1220df 100644
--- a/include/mapnik/grid/grid_util.hpp
+++ b/include/mapnik/grid/grid_util.hpp
@@ -50,7 +50,10 @@ static inline void scale_grid(mapnik::grid::data_type & target,
     int th2 = target_height/2;
     int offs_x = rint((source_width-target_width-x_off_f*2*source_width)/2);
     int offs_y = rint((source_height-target_height-y_off_f*2*source_height)/2);
-    unsigned yprt, yprt1, xprt, xprt1;
+    unsigned yprt(0);
+    unsigned yprt1(0);
+    unsigned xprt(0);
+    unsigned xprt1(0);
 
     //no scaling or subpixel offset
     if (target_height == source_height && target_width == source_width && offs_x == 0 && offs_y == 0){