diff --git a/doc/fixes37.0 b/doc/fixes37.0
index 2ead283a6..5dc248646 100644
--- a/doc/fixes37.0
+++ b/doc/fixes37.0
@@ -1,4 +1,4 @@
-NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.390 $ $NHDT-Date: 1607895902 2020/12/13 21:45:02 $
+NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.391 $ $NHDT-Date: 1607901923 2020/12/13 23:25:23 $
 
 General Fixes and Modified Features
 -----------------------------------
@@ -432,6 +432,7 @@ dwarves could sometimes pass through walls without digging their way
 fix genetic engineers dropping Schroedinger's cat box
 the checks and handling for fountains, sinks, and drawbridges were being
 	missed during liquid_flow
+monster movement flags unification allowed displacer beasts to displace Riders
 
 curses: 'msg_window' option wasn't functional for curses unless the binary
 	also included tty support
diff --git a/src/mon.c b/src/mon.c
index 06a00a4a3..ad126c6c5 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -1,4 +1,4 @@
-/* NetHack 3.7	mon.c	$NHDT-Date: 1607374002 2020/12/07 20:46:42 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.359 $ */
+/* NetHack 3.7	mon.c	$NHDT-Date: 1607901923 2020/12/13 23:25:23 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.360 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Derek S. Ray, 2015. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -1586,8 +1586,10 @@ struct monst *mtmp;
         allowflags |= UNLOCKDOOR;
     if (passes_bars(mtmp->data))
         allowflags |= ALLOW_BARS;
+#if 0   /* can't do this here; leave it for mfndpos() */
     if (is_displacer(mtmp->data))
         allowflags |= ALLOW_MDISP;
+#endif
     if (is_minion(mtmp->data) || is_rider(mtmp->data))
         allowflags |= ALLOW_SANCT;
     /* unicorn may not be able to avoid hero on a noteleport level */
@@ -1712,7 +1714,7 @@ long flag;
                     || (m_at(x, ny) && m_at(nx, y) && worm_cross(x, y, nx, ny)
                         && !m_at(nx, ny) && (nx != u.ux || ny != u.uy))))
                 continue;
-            if ((is_pool(nx, ny) == wantpool || poolok)
+            if ((poolok || is_pool(nx, ny) == wantpool)
                 && (lavaok || !is_lava(nx, ny))) {
                 int dispx, dispy;
                 boolean monseeu = (mon->mcansee
@@ -1764,6 +1766,7 @@ long flag;
                                 info[cnt] |= ALLOW_TM;
                             }
                         } else {
+                            flag &= ~ALLOW_MDISP; /* depends upon defender */
                             mmflag = flag | mm_displacement(mon, mtmp2);
                             if (!(mmflag & ALLOW_MDISP))
                                 continue;