token for computed field renders "Array"

For a custom content type, I have a computed field "Default Site" (machine name: field_default_site) that notes which site the user registered on (a.example.com, b.example.com, etc.). On a panels page I am trying to set the Canonical URL meta tag based on that value. When I use [node:field_default_site] it renders on the page as "Array" instead of the actual value.