Change number of activities shown per page?

I'm trying to change the number of activities shown on the BP activity stream.

I've had a look around the BP site, but keep getting an error. I have edited the activity-loop.php file from this:

<?php if ( bp_has_activities( bp_ajax_querystring( 'activity' ) ) ) : ?>

to this:

<?php if ( bp_has_activities( bp_ajax_querystring( 'activity', ‘per_page=5' ) ) ) : ?>

I get an error though:

Parse error: syntax error, unexpected '=' in /home/writers/public_html/wp-content/themes/website-pages-blog/activity/activity-loop.php on line 16

Any ideas on what I can do to change the number of items shown in the activity stream?

I'm using BuddyPress v1.5.1