Missing index on router table

Saw the query in #2036241: Routing system cannot handle /foo/bar and /foo/{baz} and wondered what the indexes where, turns out this isn't covered properly.

mysql> EXPLAIN SELECT * FROM router WHERE pattern_outline IN ('foo') ORDER BY fit DESC;
+----+-------------+--------+------+-----------------+-----------------+---------+-------+------+----------------------------------------------------+
| id | select_type | table  | type | possible_keys   | key             | key_len | ref   | rows | Extra                                              |
+----+-------------+--------+------+-----------------+-----------------+---------+-------+------+----------------------------------------------------+
|  1 | SIMPLE      | router | ref  | pattern_outline | pattern_outline | 767     | const |    1 | Using index condition; Using where; Using filesort |
+----+-------------+--------+------+-----------------+-----------------+---------+-------+------+----------------------------------------------------+
1 row in set (0.00 sec)