As you may have heard, MySQL utf8 is not actually utf8. It only goes up to 3 bytes instead of 4. So I converted all my databases to utf8mb4 including all the fields. But I am still getting this error occasionally. Illegal mix of collations (utf8mb4_general_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '=' I am wondering if all I need to do is change library/XenForo/Application.php on line 712 to utf8mb4. 'charset' => 'utf8'