Unable to filter on User.UserType

SELECT Id FROM Lead WHERE Owner.UserType = 'PowerPartner'

Result:

INVALID_FIELD: 
SELECT Id FROM Lead WHERE Owner.UserType = 'PowerPartner'
                          ^
ERROR at Row:1:Column:27
No such column 'UserType' on entity 'Name'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.
INVALID_FIELD: SELECT Id FROM Lead WHERE Owner.UserType = 'PowerPartner'                          ^ERROR at Row:1:Column:27No such column 'UserType' on entity 'Name'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.

What's wrong with this query?