diff --git a/utils/mapnik-index/build.py b/utils/mapnik-index/build.py
index 358ce5f88..230f545e4 100644
--- a/utils/mapnik-index/build.py
+++ b/utils/mapnik-index/build.py
@@ -33,7 +33,7 @@ source = Split(
     mapnik-index.cpp
     process_csv_file.cpp
     process_geojson_file.cpp
-    ../../plugins/input/csv/csv_utils.cpp
+    ../../plugins/input/csv/csv_utils.os
     """
     )