Unable to verify first certificate

I have a directory with certificate bundles, Python scripts and Node scripts. Both scripts make GET requests to the same URL and provide the same certificate bundle. The Python script makes the request as expected, but the node script throws this error:

{[ERROR: Unable to verify first certificate] Code: 'UNABLE_TO_VERIFY_LEAF_SIGNATURE'}

Python script (Python 3.4.3 and requests library) :

import requests
print(requests.get(url, verify='/tmp/cert/cacert.pem'))

Node script (node ​​4.2.6 and requests library) :

var fs = require('fs');
var request = require('request');

request.get({
    url: url,
    agentOptions: {
        ca: fs.readFileSync('/tmp/cert/cacert.pem')
    }
}, function (error, response, body) {
    if (error) {
        console.log(error);
    } else {
        console.log(body);
    }
});

Both use the same OpenSSL version:

$ python -c 'import ssl; print(ssl.OPENSSL_VERSION)'
OpenSSL 1.0.2e-fips 3 Dec 2015

$ node -pe process.versions.openssl 
1.0.2e

I don't think there is a problem with the certificate bundle, and I don't want to turn off host verification in Node.

Does anyone know why Node is throwing this error?