diff --git a/include/extern.h b/include/extern.h
index 0f62485d6..375acdf22 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -2677,6 +2677,7 @@ extern void selection_free(struct selectionvar *, boolean);
 extern void selection_clear(struct selectionvar *, int);
 extern struct selectionvar *selection_clone(struct selectionvar *);
 extern void selection_getbounds(struct selectionvar *, NhRect *);
+extern void selection_recalc_bounds(struct selectionvar *);
 extern void set_selection_floodfillchk(int(*)(coordxy, coordxy));
 extern void selection_floodfill(struct selectionvar *, coordxy, coordxy,
                                 boolean);
diff --git a/src/nhlsel.c b/src/nhlsel.c
index 52850d8f6..8694f7147 100644
--- a/src/nhlsel.c
+++ b/src/nhlsel.c
@@ -337,6 +337,9 @@ l_selection_xor(lua_State *L)
             int val = selection_getpoint(x, y, sela) ^ selection_getpoint(x, y, selb);
             selection_setpoint(x, y, selr, val);
         }
+    /* this may have created a smaller or irregular selection with bounds_dirty
+     * set to true - update its boundaries */
+    selection_recalc_bounds(selr);
 
     lua_remove(L, 1);
     lua_remove(L, 1);
@@ -363,6 +366,9 @@ l_selection_sub(lua_State *L)
             int val = (a_pt ^ b_pt) & a_pt;
             selection_setpoint(x, y, selr, val);
         }
+    /* this may have created a smaller or irregular selection with bounds_dirty
+     * set to true - update its boundaries */
+    selection_recalc_bounds(selr);
 
     lua_remove(L, 1);
     lua_remove(L, 1);
diff --git a/src/sp_lev.c b/src/sp_lev.c
index db20cb745..637fd3c65 100644
--- a/src/sp_lev.c
+++ b/src/sp_lev.c
@@ -124,7 +124,6 @@ static const char *get_mkroom_name(int);
 static int get_table_roomtype_opt(lua_State *, const char *, int);
 static int get_table_traptype_opt(lua_State *, const char *, int);
 static int get_traptype_byname(const char *);
-static void selection_recalc_bounds(struct selectionvar *);
 static lua_Integer get_table_intarray_entry(lua_State *, int, int);
 static struct sp_coder *sp_level_coder_init(void);
 
@@ -4562,7 +4561,7 @@ selection_getbounds(struct selectionvar *sel, NhRect *b)
 }
 
 /* recalc the boundary of selection, if necessary */
-static void
+void
 selection_recalc_bounds(struct selectionvar *sel)
 {
     coordxy x, y;