diff --git a/doc/fixes36.1 b/doc/fixes36.1
index 59d97f7b5..1fe963394 100644
--- a/doc/fixes36.1
+++ b/doc/fixes36.1
@@ -124,6 +124,7 @@ override MSGTYPE=norep while executing the ':' command
 if a chameleon took vampire form, it would stop periodically changing shape
 corpses obtained from tipping an ice box wouldn't rot away
 suppress "you climb up the stairs" message if verbose option is off
+physical damage from mind flayer attack was being inflicted twice
 
 
 Platform- and/or Interface-Specific Fixes
diff --git a/src/mhitu.c b/src/mhitu.c
index 814061ccd..d8c85a133 100644
--- a/src/mhitu.c
+++ b/src/mhitu.c
@@ -1091,9 +1091,11 @@ register struct attack *mattk;
                  helm_simple_name(uarmh));
             break;
         }
+        /* negative armor class doesn't reduce this damage */
         if (Half_physical_damage)
             dmg = (dmg + 1) / 2;
         mdamageu(mtmp, dmg);
+        dmg = 0; /* don't inflict a second dose below */
 
         if (!uarmh || uarmh->otyp != DUNCE_CAP) {
             /* eat_brains() will miss if target is mindless (won't