diff --git a/src/api.js b/src/api.js
index 249795d45..14d420eef 100644
--- a/src/api.js
+++ b/src/api.js
@@ -116,13 +116,13 @@ function resolveParams (method, params) {
 function getMethodsInfo () {
   const methods = {}
 
-  forEach(this.api._methods, function (method, name) {
+  forEach(this.api._methods, (method, name) => {
     this[name] = {
       description: method.description,
       params: method.params || {},
       permission: method.permission
     }
-  }, methods)
+  })
 
   return methods
 }
@@ -201,7 +201,8 @@ export default class Api {
 
   addMethods (methods) {
     let base = ''
-    forEach(methods, function addMethod (method, name) {
+
+    const addMethod = (method, name) => {
       name = base + name
 
       if (isFunction(method)) {
@@ -211,9 +212,10 @@ export default class Api {
 
       const oldBase = base
       base = name + '.'
-      forEach(method, addMethod, this)
+      forEach(method, addMethod)
       base = oldBase
-    }, this)
+    }
+    forEach(methods, addMethod)
   }
 
   async call (session, name, params) {
diff --git a/src/collection.js b/src/collection.js
index db1f6af41..fdf2e8fef 100644
--- a/src/collection.js
+++ b/src/collection.js
@@ -3,7 +3,7 @@ import isObject from 'lodash.isobject'
 import Model from './model'
 import {BaseError} from 'make-error'
 import {EventEmitter} from 'events'
-import {mapInPlace} from './utils'
+import {map} from './utils'
 
 // ===================================================================
 
@@ -42,7 +42,7 @@ export default class Collection extends EventEmitter {
     }
 
     const {Model} = this
-    mapInPlace(models, model => {
+    map(models, model => {
       if (!(model instanceof Model)) {
         model = new Model(model)
       }
@@ -54,7 +54,7 @@ export default class Collection extends EventEmitter {
       }
 
       return model.properties
-    })
+    }, models)
 
     models = await this._add(models, opts)
     this.emit('add', models)
@@ -103,7 +103,7 @@ export default class Collection extends EventEmitter {
     }
 
     const {Model} = this
-    mapInPlace(models, model => {
+    map(models, model => {
       if (!(model instanceof Model)) {
         // TODO: Problems, we may be mixing in some default
         // properties which will overwrite existing ones.
@@ -125,7 +125,7 @@ export default class Collection extends EventEmitter {
       }
 
       return model.properties
-    })
+    }, models)
 
     models = await this._update(models)
     this.emit('update', models)
diff --git a/src/index.js b/src/index.js
index 2c6f5bc63..98f999ab1 100644
--- a/src/index.js
+++ b/src/index.js
@@ -274,7 +274,7 @@ async function registerPlugins (xo) {
   await Promise.all(mapToArray([
     `${__dirname}/../node_modules/`,
     '/usr/local/lib/node_modules/'
-  ], registerPluginsInPath, xo))
+  ], xo::registerPluginsInPath))
 }
 
 // ===================================================================
@@ -314,7 +314,7 @@ async function makeWebServerListen ({
 async function createWebServer (opts) {
   const webServer = new WebServer()
 
-  await Promise.all(mapToArray(opts, makeWebServerListen, webServer))
+  await Promise.all(mapToArray(opts, webServer::makeWebServerListen))
 
   return webServer
 }
diff --git a/src/utils.js b/src/utils.js
index c7edea684..6a9e8b2e3 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -428,11 +428,10 @@ export const DONE = {}
 export function map (
   collection,
   iteratee,
-  thisArg,
   target = has(collection, 'length') ? [] : {}
 ) {
   forEach(collection, (item, i) => {
-    const value = iteratee.call(thisArg, item, i, collection, DONE)
+    const value = iteratee(item, i, collection, DONE)
     if (value === DONE) {
       return false
     }
@@ -443,11 +442,6 @@ export function map (
   return target
 }
 
-// Helper to `map()` to update the current collection.
-export function mapInPlace (collection, iteratee, thisArg) {
-  return map(collection, iteratee, thisArg, collection)
-}
-
 // -------------------------------------------------------------------
 
 // Create a hash from multiple values.
diff --git a/src/xo.js b/src/xo.js
index 914897ddb..51691203a 100644
--- a/src/xo.js
+++ b/src/xo.js
@@ -545,8 +545,8 @@ export default class Xo extends EventEmitter {
     group.users = userIds
 
     await Promise.all([
-      Promise.all(mapToArray(newUsers, this._users.save, this._users)),
-      Promise.all(mapToArray(oldUsers, this._users.save, this._users)),
+      Promise.all(mapToArray(newUsers, ::this._users.save)),
+      Promise.all(mapToArray(oldUsers, ::this._users.save)),
       this._groups.save(group)
     ])
   }