1 files changed, 2 insertions, 0 deletions
diff --git a/pp_sys.c b/pp_sys.c
index 91b9d772dc..11cd863470 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -13,6 +13,8 @@
  * cloven by a great fissure, out of which the red glare came, now leaping
  * up, now dying down into darkness; and all the while far below there was
  * a rumour and a trouble as of great engines throbbing and labouring.
+ *
+ *     [p.945 of _The Lord of the Rings_, VI/iii: "Mount Doom"]
  */
 
 /* This file contains system pp ("push/pop") functions that