Express morgan logging fails to skip logging keep-alive requests

I am running a node.js express app in AWS behind an Elastic Load Balancer. I am using 'morgan' as my logging mechanism.

ELB sends a keep-alive request periodically, the target of which I have defined as a 1 char text file (keep-alive.txt).

Obviously, I don't want to see these requests in the log, so I have used the morgan skip function as follows:

// use morgan to log requests to the console
var morganOptions = {
    skip: function (req, res) {
        return req.get('/keep-alive.txt');  // don't log the load balancer keep alive pings
    }
};
app.use(logger('dev', morganOptions));

According to the morgan doc, returning TRUE to the skip function should cause the log skip. However, morgan is logging every keep-alive fetch. What am I doing wrong?

via RustyB