diff --git a/Makefile b/Makefile
index 16d9d974b..8f30a9114 100755
--- a/Makefile
+++ b/Makefile
@@ -22,13 +22,13 @@ mapnik:
 		src/expression_grammar.os \
 		src/transform_expression_grammar.os \
 		src/image_filter_types.os \
-		src/renderer_common/process_group_symbolizer.cpp \
-		src/agg/process_markers_symbolizer.cpp \
-		src/agg/process_group_symbolizer.cpp \
-		src/grid/process_markers_symbolizer.cpp \
-		src/grid/process_group_symbolizer.cpp \
-		src/cairo/process_markers_symbolizer.cpp \
-		src/cairo/process_group_symbolizer.cpp \
+		src/renderer_common/process_group_symbolizer.os \
+		src/agg/process_markers_symbolizer.os \
+		src/agg/process_group_symbolizer.os \
+		src/grid/process_markers_symbolizer.os \
+		src/grid/process_group_symbolizer.os \
+		src/cairo/process_markers_symbolizer.os \
+		src/cairo/process_group_symbolizer.os \
 	# then install the rest with -j$(JOBS)
 	$(PYTHON) scons/scons.py -j$(JOBS) --config=cache --implicit-cache --max-drift=1