Slope tileh_end_aqueduct = GetTileSlope(tile_end);
			if (tileh_end_aqueduct != ComplementSlope(tileh_start)) {
				switch (tileh_start) {
					case SLOPE_NE:
						switch (tileh_end_aqueduct) {
							case SLOPE_S:
							case SLOPE_STEEP_S:
								tileh_end_aqueduct = SLOPE_W;
								break;
							case SLOPE_W:
							case SLOPE_STEEP_W:
								tileh_end_aqueduct = SLOPE_S;
								break;
							default: NOT_REACHED();
						}
					case SLOPE_NW:
						switch (tileh_end_aqueduct) {
							case SLOPE_E:
							case SLOPE_STEEP_E:
								tileh_end_aqueduct = SLOPE_S;
								break;
							case SLOPE_S:
							case SLOPE_STEEP_S:
								tileh_end_aqueduct = SLOPE_E;
								break;
							default: NOT_REACHED();
						}
					case SLOPE_SW:
						switch (tileh_end_aqueduct) {
							case SLOPE_N:
							case SLOPE_STEEP_N:
								tileh_end_aqueduct = SLOPE_E;
								break;
							case SLOPE_E:
							case SLOPE_STEEP_E:
								tileh_end_aqueduct = SLOPE_N;
								break;
							default: NOT_REACHED();
						}
					case SLOPE_SE:
						switch (tileh_end_aqueduct) {
							case SLOPE_W:
							case SLOPE_STEEP_W:
								tileh_end_aqueduct = SLOPE_N;
								break;
							case SLOPE_N:
							case SLOPE_STEEP_N:
								tileh_end_aqueduct = SLOPE_W;
								break;
							default: NOT_REACHED();
						}
					default: NOT_REACHED();
				}
				/* Mark the tile as already cleared for the terraform command.
				* Do this for all tiles (like trees), not only objects. */
				ClearedObjectArea *coa = FindClearedObject(tile_end);
				if (coa == NULL) {
					coa = _cleared_object_areas.Append();
					coa->first_tile = tile_end;
					coa->area = TileArea(tile_end, 1, 1);
				}

				/* Hide the tile from the terraforming command */
				TileIndex old_first_tile = coa->first_tile;
				coa->first_tile = INVALID_TILE;
				ret = DoCommand(tile_end, tileh_end_aqueduct, 1, flags, CMD_TERRAFORM_LAND);
				coa->first_tile = old_first_tile;
				if (ret.Failed()) return_cmd_error(STR_ERROR_UNABLE_TO_EXCAVATE_LAND);
				cost.AddCost(ret);
			}