Google Pagespeed and CNAME

I'm trying to set my Linode to work with the Google Pagespeed service. Google's instructions instruct me to set my CNAME DNS record to have a hostname = www, and the ALIAS as pagespeed.googlehosted.com.

However, everytime I try to add this CNAME record in the Linode DNS manager i get the error "Record conflict - CNAMES must be unique". I'm using the default DNS settings that are generated by Linode. I tried using a different hostname other than "www" and it allowed me to add it, but google pagespeed did not recognise it.

Any one have experience with this?