reverse dns - Hotmail wants me to modify my SPF record

This is my current SPF record. It works well with gmail and yahoo but hotmail was ignoring. So i used their submit system and now they replied me with the text below.

This is my current spf

v=spf1 a mx ptr ~all

Now this is hotmail message

We have successfully added your domain to the Sender ID program. This may take up to 2 business days to be fully replicated in our systems. If you have any questions regarding this please let me know.

We reviewed your SPF record and note that it includes the "ptr" or reverse DNS lookup mechanism. The specification for SPF records (RFC 4408) discourages use of "ptr" for performance and reliability reasons. This is especially important for Windows Live Mail, Hotmail and other large ISPs as a result of the very high volume of mail we receive each day. We highly recommend you remove the "ptr" mechanism from your SPF record and, if necessary, replace it with other SPF mechanisms that do not require a reverse DNS lookup, such as "a", "mx", "ip4" and "include." This will help ensure that Sender ID validation is performed as accurately as possible, maximizing your email deliverability while protecting your domain from spoofing.

So my question is simple. What is the corrected way of it to make it as hotmail wants. Thank you.

Hotmail received email from my server headers

Authentication-Results: hotmail.com; 
sender-id=temperror (sender IP is 85.17.154.139) 
header.from=noreply@monstermmorpg.com; 
dkim=pass 
header.d=monstermmorpg.com; 
x-hmca=pass
X-Message-Status: n:0:n

X-SID-PRA: MonsterMMORPG 

Answer

In your case, the same string you're using minus the ptr should do the trick.

v=spf1 a mx ~all