ERROR 3021 (HY000): This operation cannot be performed with a running slave io thread; run STOP SLAVE IO_THREAD

mysql> CHANGE MASTER TO MASTER_HOST='10.146.0.18',
    -> MASTER_USER='rpl_user',
    -> MASTER_PASSWORD='password',
    -> MASTER_LOG_FILE='mysql-bin.000091',
    -> MASTER_LOG_POS=1372;
ERROR 3021 (HY000): This operation cannot be performed with a running slave io thread; run STOP SLAVE IO_THREAD FOR
 CHANNEL '' first.

というエラーが出たので、

mysql> STOP SLAVE;

mysql> CHANGE MASTER TO MASTER_HOST='10.146.0.18',
    -> MASTER_USER='rpl_user',
    -> MASTER_PASSWORD='password',
    -> MASTER_LOG_FILE='mysql-bin.000091',
    -> MASTER_LOG_POS=1372;
Query OK, 0 rows affected, 2 warnings (0.03 sec)

mysql> START SLAVE;

と対応した。