diff --git a/src/dig.c b/src/dig.c
index f3e9ed22b..b3a1bd8dd 100644
--- a/src/dig.c
+++ b/src/dig.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6	dig.c	$NHDT-Date: 1431192766 2015/05/09 17:32:46 $  $NHDT-Branch: master $:$NHDT-Revision: 1.90 $ */
+/* NetHack 3.6	dig.c	$NHDT-Date: 1431563241 2015/05/14 00:27:21 $  $NHDT-Branch: master $:$NHDT-Revision: 1.91 $ */
 /* NetHack 3.6	dig.c	$Date: 2012/02/16 03:01:37 $  $Revision: 1.67 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -1272,14 +1272,21 @@ register struct monst *mtmp;
         }
         newsym(mtmp->mx, mtmp->my);
         return FALSE;
+    } else if (here->typ == SCORR) {
+        here->typ = CORR;
+        unblock_point(mtmp->mx, mtmp->my);
+        newsym(mtmp->mx, mtmp->my);
+        You_feel("a draft.");
+        return FALSE;
     } else if (!IS_ROCK(here->typ) && !IS_TREE(here->typ)) /* no dig */
         return FALSE;
 
     /* Only rock, trees, and walls fall through to this point. */
     if ((here->wall_info & W_NONDIGGABLE) != 0) {
         impossible("mdig_tunnel:  %s at (%d,%d) is undiggable",
-                   (IS_WALL(here->typ) ? "wall" : "stone"), (int) mtmp->mx,
-                   (int) mtmp->my);
+                   (IS_WALL(here->typ) ? "wall"
+                    : IS_TREE(here->typ) ? "tree" : "stone"),
+                   (int) mtmp->mx, (int) mtmp->my);
         return FALSE; /* still alive */
     }
 
diff --git a/src/hack.c b/src/hack.c
index f923da9d3..7c3213594 100644
--- a/src/hack.c
+++ b/src/hack.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6	hack.c	$NHDT-Date: 1431192758 2015/05/09 17:32:38 $  $NHDT-Branch: master $:$NHDT-Revision: 1.148 $ */
+/* NetHack 3.6	hack.c	$NHDT-Date: 1431563243 2015/05/14 00:27:23 $  $NHDT-Branch: master $:$NHDT-Revision: 1.149 $ */
 /* NetHack 3.6	hack.c	$Date: 2013/10/26 21:33:47 $  $Revision: 1.120 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -580,13 +580,15 @@ dosinkfall()
     float_vs_flight();
 }
 
+/* intended to be called only on ROCKs or TREEs */
 boolean
 may_dig(x, y)
 register xchar x, y;
-/* intended to be called only on ROCKs */
 {
-    return (boolean)(!(IS_STWALL(levl[x][y].typ)
-                       && (levl[x][y].wall_info & W_NONDIGGABLE)));
+    struct rm *lev = &levl[x][y];
+
+    return (boolean)(!((IS_STWALL(lev->typ) || IS_TREE(lev->typ))
+                       && (lev->wall_info & W_NONDIGGABLE)));
 }
 
 boolean
diff --git a/src/mon.c b/src/mon.c
index d2f494908..189ae52b8 100644
--- a/src/mon.c
+++ b/src/mon.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6	mon.c	$NHDT-Date: 1431192769 2015/05/09 17:32:49 $  $NHDT-Branch: master $:$NHDT-Revision: 1.174 $ */
+/* NetHack 3.6	mon.c	$NHDT-Date: 1431563243 2015/05/14 00:27:23 $  $NHDT-Branch: master $:$NHDT-Revision: 1.175 $ */
 /* NetHack 3.6	mon.c	$Date: 2012/05/16 02:15:10 $  $Revision: 1.126 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -1114,11 +1114,12 @@ long flag;
             treeok = (m_carrying(mon, AXE) || (m_carrying(mon, BATTLE_AXE)
                                                && !which_armor(mon, W_ARMS)));
         }
-        thrudoor |= rockok || treeok;
+        if (rockok || treeok)
+            thrudoor = TRUE;
     }
 
 nexttry: /* eels prefer the water, but if there is no water nearby,
-    they will crawl over land */
+            they will crawl over land */
     if (mon->mconf) {
         flag |= ALLOW_ALL;
         flag &= ~NOTONL;
@@ -1131,7 +1132,8 @@ nexttry: /* eels prefer the water, but if there is no water nearby,
         for (ny = max(0, y - 1); ny <= maxy; ny++) {
             if (nx == x && ny == y)
                 continue;
-            if (IS_ROCK(ntyp = levl[nx][ny].typ)
+            ntyp = levl[nx][ny].typ;
+            if (IS_ROCK(ntyp)
                 && !((flag & ALLOW_WALL) && may_passwall(nx, ny))
                 && !((IS_TREE(ntyp) ? treeok : rockok) && may_dig(nx, ny)))
                 continue;
diff --git a/src/monmove.c b/src/monmove.c
index 1e1ea7280..70787c7cc 100644
--- a/src/monmove.c
+++ b/src/monmove.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6	monmove.c	$NHDT-Date: 1431195533 2015/05/09 18:18:53 $  $NHDT-Branch: master $:$NHDT-Revision: 1.69 $ */
+/* NetHack 3.6	monmove.c	$NHDT-Date: 1431563244 2015/05/14 00:27:24 $  $NHDT-Branch: master $:$NHDT-Revision: 1.70 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -1100,9 +1100,9 @@ not_special:
         if (mmoved == 1 && (u.ux != nix || u.uy != niy) && itsstuck(mtmp))
             return (3);
 
-        if (((IS_ROCK(levl[nix][niy].typ) && may_dig(nix, niy))
-             || closed_door(nix, niy)) && mmoved == 1
-            && can_tunnel && needspick(ptr)) {
+        if (mmoved == 1 && can_tunnel && needspick(ptr)
+            && ((IS_ROCK(levl[nix][niy].typ) && may_dig(nix, niy))
+                || closed_door(nix, niy))) {
             if (closed_door(nix, niy)) {
                 if (!(mw_tmp = MON_WEP(mtmp)) || !is_pick(mw_tmp)
                     || !is_axe(mw_tmp))