mysql> describe test;
+----------+------------------+------+-----+---------+-------+
| Field    | Type             | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+-------+
| leechers | int(10) unsigned | YES  |     | NULL    |       |
+----------+------------------+------+-----+---------+-------+
1 row in set (0.00 sec)

mysql> insert into test values(0);
Query OK, 1 row affected (0.00 sec)

mysql> update test set leechers = leechers - 1;
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 1

mysql> select * from test;
+------------+
| leechers   |
+------------+
| 4294967295 |
+------------+
1 row in set (0.00 sec)