A closed set of CGL equations, modified to include heat flux correction, is used to study the firehose and mirror instabilities in a rarefied plasma. A significant feature which has been noticed is that some of the terms contributed by the higher-order moments are of the same order as the terms in the unmodified CGL equations. We study the effect on the firehose and mirror instabilities of those terms which persist in the limit of vanishing heat flux vector. It is found that these terms lead to a new criterion for mirror instability. The criterion for hose instability, however, remains unaffected.