--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -69,7 +69,7 @@
 /*
  * DISABLE_LEADER_PARTICIPATION disables the leader's participation in
  * parallel index builds.  This may be useful as a debugging aid.
-#undef DISABLE_LEADER_PARTICIPATION
+ *#undef DISABLE_LEADER_PARTICIPATION
  */