Is it OK to call clearInterval inside a setInterval handler?

I have a piece of Javascript that checks for a condition (via an AJAX call) every n seconds. If that condition is true, it stops checking. I have implemented it in the following way:

var stopTimer;
var timerId = setInterval(function() {

    /* Make Ajax Calls and set stopTimer */

    if (stopTimer) {
        clearInterval(timerId);
    }
}, 10000);

However, I find erratic behaviour: Works sometimes, but at other times, it keeps checking forever. I have checked that (as much as is possible) there is no error in any part of the code.

I am therefore suspecting that calling clearInterval inside a setInterval handler might be the culprit. Is that right? Is it OK to call clearInterval inside a setInterval handler?

Thank you for your attention