diff --git a/base/Makefile b/base/Makefile
index 1823c9b49..ff7781577 100644
--- a/base/Makefile
+++ b/base/Makefile
@@ -11,7 +11,8 @@
 # Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
 # Uncomment this to build the simple radix tree.  You'll need to make clean too.
-# base/data-struct/radix-tree.o: CFLAGS += -DSIMPLE_RADIX_TREE
+# Comment to build the advanced radix tree.
+base/data-struct/radix-tree.o: CFLAGS += -DSIMPLE_RADIX_TREE
 
 BASE_SOURCE=\
 	base/data-struct/radix-tree.c \