Get SUM() from mysql JOIN query

I am trying to get a sum(vote_amount) from a joined table 'votes' in this mysql query. Unfortunately it gives me an error. How do I get this query to work?

SELECT d.discussion_id, d.discussion_google_id, d.discussion_title, d.discussion_text, d.discussion_views, d.discussion_last_view_ip, d.discussion_created, d.discussion_updated, u.google_picture_link, v.sum(vote_amount)
FROM discussions AS d
INNER JOIN google_users AS u
ON u.google_id = d.discussion_google_id
INNER JOIN votes AS v
ON v.vote_discussion_id = d.discussion_id
WHERE d.discussion_deleted = 0

The error it gives is:

#1630 - FUNCTION v.sum does not exist. Check the 'Function Name Parsing and Resolution' section in the Reference Manual