Postfix, SPF, and Perl: warning: premature end-of-input on private/policy while reading input attribute name

I followed this guide (http://www.thenoccave.com/2013/05/08/centos-6-postfix-spf-checking/) but I'm getting the following errors in maillog:

May  8 22:15:13 ip-172-31-15-65 postfix/smtpd[1999]: warning: premature end-of-input on private/policy while reading input attribute name
May  8 22:15:14 ip-172-31-15-65 postfix/spawn[2037]: warning: command /usr/bin/perl exit status 2
May  8 22:15:14 ip-172-31-15-65 postfix/smtpd[1999]: warning: premature end-of-input on private/policy while reading input attribute name
May  8 22:15:14 ip-172-31-15-65 postfix/smtpd[1999]: warning: problem talking to server private/policy: Connection reset by peer

Here is part of main.cf

smtpd_recipient_restrictions = reject_non_fqdn_sender,
  reject_non_fqdn_recipient,
  reject_unknown_recipient_domain,
  permit_sasl_authenticated,
  reject_unauth_destination,
  permit_inet_interfaces,
  check_policy_service unix:postgrey/socket,
  check_policy_service unix:private/policy policy_time_limit = 3600s

Here is part of master.cf

policy  unix  -       n       n       -       -       spawn user=nobody argv=/usr/bin/perl /usr/lib/postfix-policyd-spf-perl

I also tried

  check_policy_service unix:postgrey/socket,
  check_policy_service unix:private/policy,
  policy_time_limit = 3600s

Here is the full master.cf.

postfix check doesn't report any errors.

There was a similar question, but it was for Debian and Python.

CentOS 6.6, postfix-policyd-spf-perl 2.01.