diff --git a/src/mon.c b/src/mon.c
index 0900ebe22..a8837d127 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -1119,7 +1119,7 @@ mcalcmove(
     if (mon->mspeed == MSLOW) {
         /* slow-monster effects work better against faster monsters: they
            lose 1/3 of their speed below 12 but 2/3 of their speed above */
-        if (mmove < 12)
+        if (mmove < NORMAL_SPEED)
             mmove = (2 * mmove + 1) / 3;
         else
             mmove = 4 + (mmove / 3);