Node.js Secure Random Float from Crypto Buffer

Not for any practical purpose, of course, but I tried to generate a secure random floating point number using the Node's crypto module. Essentially, the following:

var crypto = require('crypto');
var buf = crypto.randomBytes(4);
var float = buf.readFloatBE();

This doesn't work, as far as the following test can tell, in an average of 0.40% of cases. Instead of getting a float, I get NaN.

var colors = require('colors');
var crypto = require('crypto');

var buf = new Buffer(4);
var fails = 0, tries = 100000;
var failures = [];

for (var i = 0; i < tries; i++) {
    var num = crypto.randomBytes(4).readFloatBE(0);
    try {
        buf.writeFloatBE(num, 0);
    } catch (e) {
        fails++;
        failures.push(buf.readUInt32BE(0).toString(2));
    }
}

var percent = 100 * fails / tries;
if (fails)
    percent = (percent.toFixed(2) + "%").red;
else
    percent = '0.00%'.blue.bold;
console.log('Test ' + 'complete'.green.bold + ', ' + percent + ": " + fails + " / " + tries);
fails && console.log('Failed'.red + ' values:', failures.join(', '));

I'm guessing this is due to the IEEE single precision floating point number specification, but I'm not familiar with exactly how the float is stored as binary.

Why does this happen, exactly, and apart from simply generating floats until I get a valid number, how can I circumvent this?

EDIT: when looking at the filtered binary data, it appears they all follow the same pattern: the first 8 bits are all set. Everything else is random.