diff --git a/src/sp_lev.c b/src/sp_lev.c
index 81d7c136f..73411d4fc 100644
--- a/src/sp_lev.c
+++ b/src/sp_lev.c
@@ -5564,7 +5564,9 @@ lspo_replace_terrain(lua_State *L)
                     if (mapfrag_match(mf, x, y) && (rn2(100)) < chance)
                         (void) set_levltyp_lit(x, y, totyp, tolit);
                 } else {
-                    if (levl[x][y].typ == fromtyp && rn2(100) < chance)
+                    if (((fromtyp == MATCH_WALL && IS_STWALL(levl[x][y].typ))
+                         || levl[x][y].typ == fromtyp)
+                        && rn2(100) < chance)
                         (void) set_levltyp_lit(x, y, totyp, tolit);
                 }
             }