MySQL overflow error possible

From notifications_event_tracker() in notifications.cron.inc:

385  case 'update':
386        foreach ($events as $eid => $count) {
387          db_query('UPDATE {notifications_event} SET counter = counter - %d WHERE eid = %d', $count, $eid);
388        }

I encountered this by chance and have yet to be able to reproduce the conditions that caused it (I'll update this if I do). At some point on my site, this update statement tried to set the counter to a value below zero, which is a problem since counter is unsigned. As of MySQL 5.5.5, this will generate the error "BIGINT UNSIGNED value is out of range in ..." (see bottom of http://dev.mysql.com/doc/refman/5.5/en/out-of-range-and-overflow.html)

Regardless of how this error might have happened, there should be protection in place to prevent a value less than zero from being assigned to counter. Maybe something along the lines of

db_query('UPDATE {notifications_event} SET counter = GREATEST(counter - %d, 0) WHERE eid = %d', $count, $eid);