Get pr diff using oauth1 API returns 401 (BB-11086)

I'm trying to get the diff of a pull request using one of the links that is returned from:
https://bitbucket.org/api/2.0/repositories/USER/REPO/pullrequests/ID

Which returns a link for getting a diff for the pull request:

https://bitbucket.org/api/2.0/repositories/USER/REPO/pullrequests/ID/diff

But when I make this request with oauth authentication it returns a 401 status code? This url works fine when I use by bitbucket session from a browser, but not with oauth.

Thanks!