diff --git a/doc/fixes34.2 b/doc/fixes34.2
index f80ba3b72..49eba3559 100644
--- a/doc/fixes34.2
+++ b/doc/fixes34.2
@@ -68,6 +68,7 @@ poison missiles were unintentionally more likely to inflict "deadly poison"
 provide feedback when going invisible after eating a stalker
 killer on tombstone had no prefix for starvation/exhaustion case
 ensure proper message ordering for boulder trap messages
+clean up data set by join_map that is overlaid by MAPs on special levels
 
 
 Platform- and/or Interface-Specific Fixes
diff --git a/include/extern.h b/include/extern.h
index 2356a1950..24d9538f2 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -1011,6 +1011,7 @@ E void NDECL(mkinvokearea);
 /* ### mkmap.c ### */
 
 void FDECL(flood_fill_rm, (int,int,int,BOOLEAN_P,BOOLEAN_P));
+void FDECL(remove_rooms, (int,int,int,int));
 
 /* ### mkmaze.c ### */
 
diff --git a/src/mkmap.c b/src/mkmap.c
index f9a68d68b..7b94dfa33 100644
--- a/src/mkmap.c
+++ b/src/mkmap.c
@@ -17,6 +17,7 @@ STATIC_DCL void FDECL(pass_three,(SCHAR_P,SCHAR_P));
 STATIC_DCL void NDECL(wallify_map);
 STATIC_DCL void FDECL(join_map,(SCHAR_P,SCHAR_P));
 STATIC_DCL void FDECL(finish_map,(SCHAR_P,SCHAR_P,XCHAR_P,XCHAR_P));
+STATIC_DCL void FDECL(remove_room,(int));
 void FDECL(mkmap, (lev_init *));
 
 char *new_locations;
@@ -361,13 +362,91 @@ finish_map(fg_typ, bg_typ, lit, walled)
 		    levl[i][j].lit = TRUE;
 }
 
+/*
+ * When level processed by join_map is overlaid by a MAP, some rooms may no
+ * longer be valid.  All rooms in the region lx <= x < hx, ly <= y < hy are
+ * removed.  Rooms partially in the region are truncated.  This function
+ * must be called before the REGIONs or ROOMs of the map are processed, or
+ * those rooms will be removed as well.  Assumes roomno fields in the
+ * region are already cleared, and roomno and irregular fields outside the
+ * region are all set.
+ */
+void
+remove_rooms(lx, ly, hx, hy)
+    int lx, ly, hx, hy;
+{
+    int i;
+    struct mkroom *croom;
+
+    for (i = nroom - 1; i >= 0; --i) {
+	croom = &rooms[i];
+	if (croom->hx < lx || croom->lx >= hx ||
+	    croom->hy < ly || croom->ly >= hy) continue; /* no overlap */
+
+	if (croom->lx < lx || croom->hx >= hx ||
+	    croom->ly < ly || croom->hy >= hy) { /* partial overlap */
+	    /* TODO: ensure remaining parts of room are still joined */
+
+	    if (!croom->irregular) impossible("regular room in joined map");
+
+	    /* if a "donut" or even disconnected room, leave bounds alone */
+	    if ((croom->lx < lx && croom->hx >= hx) ||
+		(croom->ly < ly && croom->hy >= hy)) {
+		continue;
+	    }
+
+	    /* truncate the side(s) that are covered by the region */
+	    if (croom->lx < lx && croom->hx < hx) croom->hx = lx - 1;
+	    if (croom->lx >= lx && croom->hx >= hx) croom->lx = hx;
+	    if (croom->ly < ly && croom->hy < hy) croom->hy = ly - 1;
+	    if (croom->ly >= ly && croom->hy >= hy) croom->ly = hy;
+	} else {
+	    /* total overlap, remove the room */
+	    remove_room(i);
+	}
+    }
+}
+
+/*
+ * Remove roomno from the rooms array, decrementing nroom.  Also updates
+ * all level roomno values of affected higher numbered rooms.  Assumes
+ * level structure contents corresponding to roomno have already been reset.
+ * Currently handles only the removal of rooms that have no subrooms.
+ */
+void
+remove_room(roomno)
+    int roomno;
+{
+    struct mkroom *croom = &rooms[roomno];
+    struct mkroom *maxroom = &rooms[--nroom];
+    int i, j, oroomno;
+
+    if (croom != maxroom) {
+	/* since the order in the array only matters for making corridors,
+	 * copy the last room over the one being removed on the assumption
+	 * that corridors have already been dug. */
+	(void) memcpy((genericptr_t)croom, (genericptr_t)maxroom,
+		      sizeof(struct mkroom));
+
+	/* since maxroom moved, update affected level roomno values */
+	oroomno = nroom + ROOMOFFSET;
+	roomno += ROOMOFFSET;
+	for (i = croom->lx; i <= croom->hx; ++i)
+	    for (j = croom->ly; j <= croom->hy; ++j) {
+		if (levl[i][j].roomno == oroomno)
+		    levl[i][j].roomno = roomno;
+	    }
+    }
+
+    maxroom->hx = -1;			/* just like add_room */
+}
+
 #define N_P1_ITER	1	/* tune map generation via this value */
 #define N_P2_ITER	1	/* tune map generation via this value */
 #define N_P3_ITER	2	/* tune map smoothing via this value */
 
 void
 mkmap(init_lev)
-
 	lev_init	*init_lev;
 {
 	schar	bg_typ = init_lev->bg,
diff --git a/src/sp_lev.c b/src/sp_lev.c
index 5aa102742..435609f3e 100644
--- a/src/sp_lev.c
+++ b/src/sp_lev.c
@@ -2167,6 +2167,11 @@ dlb *fd;
 		for(x = xstart; x < xstart+xsize; x++) {
 		    levl[x][y].typ = Fgetc(fd);
 		    levl[x][y].lit = FALSE;
+		    /* clear out levl: load_common_data may set them */
+		    levl[x][y].flags = 0;
+		    levl[x][y].horizontal = 0;
+		    levl[x][y].roomno = 0;
+		    levl[x][y].edge = 0;
 		    /*
 		     * Note: Even though levl[x][y].typ is type schar,
 		     *	 lev_comp.y saves it as type char. Since schar != char
@@ -2198,6 +2203,8 @@ dlb *fd;
 			has_bounds = TRUE;
 		    Map[x][y] = 1;
 		}
+	    if (init_lev.init_present && init_lev.joined)
+		remove_rooms(xstart, ystart, xstart+xsize, ystart+ysize);
 	}
 
 	Fread((genericptr_t) &n, 1, sizeof(n), fd);
diff --git a/util/lev_comp.y b/util/lev_comp.y
index e4cb51000..a12c7cd64 100644
--- a/util/lev_comp.y
+++ b/util/lev_comp.y
@@ -274,6 +274,9 @@ lev_init	: /* nothing */
 			    yyerror("Invalid background type.");
 			init_lev.smoothed = $7;
 			init_lev.joined = $9;
+			if (init_lev.joined &&
+			    init_lev.fg != CORR && init_lev.fg != ROOM)
+			    yyerror("Invalid foreground type for joined map.");
 			init_lev.lit = $11;
 			init_lev.walled = $13;
 			$$ = 1;