diff --git a/packages/core/parcel/src/utils/cpuCount.js b/packages/core/parcel/src/utils/cpuCount.js
new file mode 100644
index 00000000000..d0d5613075a
--- /dev/null
+++ b/packages/core/parcel/src/utils/cpuCount.js
@@ -0,0 +1,11 @@
+const os = require('os');
+
+module.exports = function() {
+  let cores;
+  try {
+    cores = require('physical-cpu-count');
+  } catch (err) {
+    cores = os.cpus().length;
+  }
+  return cores || 1;
+};
diff --git a/packages/core/parcel/src/workerfarm/Worker.js b/packages/core/parcel/src/workerfarm/Worker.js
index 8c9524984ae..e51cffc1460 100644
--- a/packages/core/parcel/src/workerfarm/Worker.js
+++ b/packages/core/parcel/src/workerfarm/Worker.js
@@ -41,7 +41,7 @@ class Worker extends EventEmitter {
 
     this.child = childProcess.fork(childModule, process.argv, options);
 
-    this.child.on('message', this.receive.bind(this));
+    this.child.on('message', data => this.receive(data));
 
     this.child.once('exit', code => {
       this.exitCode = code;
diff --git a/packages/core/parcel/src/workerfarm/WorkerFarm.js b/packages/core/parcel/src/workerfarm/WorkerFarm.js
index 316c9942450..f9e82e20b4d 100644
--- a/packages/core/parcel/src/workerfarm/WorkerFarm.js
+++ b/packages/core/parcel/src/workerfarm/WorkerFarm.js
@@ -1,7 +1,7 @@
 const {EventEmitter} = require('events');
-const os = require('os');
 const errorUtils = require('./errorUtils');
 const Worker = require('./Worker');
+const cpuCount = require('../utils/cpuCount');
 
 let shared = null;
 class WorkerFarm extends EventEmitter {
@@ -60,7 +60,7 @@ class WorkerFarm extends EventEmitter {
   }
 
   mkhandle(method) {
-    return function(...args) {
+    return (...args) => {
       // Child process workers are slow to start (~600ms).
       // While we're waiting, just run on the main thread.
       // This significantly speeds up startup time.
@@ -73,7 +73,7 @@ class WorkerFarm extends EventEmitter {
 
         return this.localWorker[method](...args, false);
       }
-    }.bind(this);
+    };
   }
 
   onError(error, worker) {
@@ -258,17 +258,9 @@ class WorkerFarm extends EventEmitter {
   }
 
   static getNumWorkers() {
-    if (process.env.PARCEL_WORKERS) {
-      return parseInt(process.env.PARCEL_WORKERS, 10);
-    }
-
-    let cores;
-    try {
-      cores = require('physical-cpu-count');
-    } catch (err) {
-      cores = os.cpus().length;
-    }
-    return cores || 1;
+    return process.env.PARCEL_WORKERS
+      ? parseInt(process.env.PARCEL_WORKERS, 10)
+      : cpuCount();
   }
 
   static callMaster(request, awaitResponse = true) {
@@ -285,7 +277,7 @@ class WorkerFarm extends EventEmitter {
   }
 
   static getConcurrentCallsPerWorker() {
-    return parseInt(process.env.PARCEL_MAX_CONCURRENT_CALLS) || 5;
+    return parseInt(process.env.PARCEL_MAX_CONCURRENT_CALLS, 10) || 5;
   }
 }