Redmine

Hi, i need some help, i need to put the custom field in the issue list, well, this is kind easy, but i need sort it too, and when i put the sort_header_tag and click to sort, it gives a error message saying

Mysql::Error: Unknown column 'custom_values.value' in 'order clause': SELECT `issues`.`id` AS t0_r0, `issues`.`tracker_id` AS t0_r1, `issues`.`project.....

Where can i alter the sql statement to find the custom_values? I was looking for it but im lost

Thanks!