keepalived: How to only demote master if a backup can take over?

I am currently trying to setup a highly available system using keepalived . I have a check-script that returns rc=0 if the host it is executed on is the master. Unfortunately this script can fail for various reasons which will lead to the demotion of the host and thus the removal of the virtual ip. I think there should be a mechanism that the current master will only be demoted if a backup is ready to take over. Unfortunately I was not able to find out if this feature is available and how to set it up. Maybe somebody can help me out?