• Version:v6.9.4
• Platform:Darwin Daves-MacBook-Air-2.local 14.3.0 Darwin Kernel Version 14.3.0: Mon Mar 23 11:59:05 PDT 2015; root:xnu-2782.20.48~5/RELEASE_X86_64 x86_64
• Subsystem:

let worker = cluster.fork();
let myMap = new Map();
myMap.set('s', {foo: 'bar'});
worker.send({
  myMap: myMap
});

When the worker gets the message myMap becomes {}
When sending an array or object it works as expected