diff --git a/include/mapnik/span_image_filter.hpp b/include/mapnik/span_image_filter.hpp
index 972558ccf..8559394fa 100644
--- a/include/mapnik/span_image_filter.hpp
+++ b/include/mapnik/span_image_filter.hpp
@@ -81,7 +81,7 @@ public:
 
             int src_x = x >> agg::image_subpixel_shift;
             int src_y = y >> agg::image_subpixel_shift;
-            const value_type* pix = reinterpret_cast<const value_type*>(base_type::source().span(src_x, src_y, 0));
+            const value_type* pix = reinterpret_cast<const value_type*>(base_type::source().span(src_x, src_y, 1));
             if (nodata_value_ && *nodata_value_ == *pix)
             {
                 span->v = *nodata_value_;