diff --git a/src/mon.c b/src/mon.c
index 68565164a..89ae78b82 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -1,4 +1,4 @@
-/* NetHack 3.7	mon.c	$NHDT-Date: 1655065140 2022/06/12 20:19:00 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.436 $ */
+/* NetHack 3.7	mon.c	$NHDT-Date: 1679896593 2023/03/27 05:56:33 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.491 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Derek S. Ray, 2015. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -3638,15 +3638,14 @@ m_respond(struct monst* mtmp)
             pline("%s shrieks.", Monnam(mtmp));
             stop_occupation();
         }
-        if (!rn2(10)) {
-            if (!rn2(13)) {
-                /* don't generate purple worms if too difficult */
-                int pm = montoostrong(PM_PURPLE_WORM, monmax_difficulty_lev())
-                         ? PM_BABY_PURPLE_WORM : PM_PURPLE_WORM;
-
-                (void) makemon(&mons[pm], 0, 0, NO_MM_FLAGS);
-            } else
-                (void) makemon((struct permonst *) 0, 0, 0, NO_MM_FLAGS);
+        if (!rn2(10)) { /* 1/10 chance per shriek to create a monster */
+            /* new monster has a 1/13 chance to be a purple worm, random
+               otherwise; baby purple worm if adult is too difficult */
+            (void) makemon(rn2(13) ? (struct permonst *) 0
+                           : &mons[montoostrong(PM_PURPLE_WORM,
+                                                monmax_difficulty_lev())
+                                   ? PM_BABY_PURPLE_WORM : PM_PURPLE_WORM],
+                           0, 0, NO_MM_FLAGS);
         }
         aggravate();
     }