diff -u -r1.17 dungeon.c
--- dungeon.c	2001/02/03 18:19:07	1.17
+++ dungeon.c	2001/03/17 19:54:51
@@ -2317,6 +2317,9 @@
 			{
 				cave_set_feat(py, px, FEAT_LESS);
 			}
+
+			/* Mark the stairs as known */
+			cave_info[py][px] |= (CAVE_MARK);
 		}
 
 		/* Cancel the stair request */