diff --git a/common/index.js b/common/index.js
index 35785e2145..6aca241e03 100644
--- a/common/index.js
+++ b/common/index.js
@@ -1,4 +1,6 @@
-var pathToCommon;
+'use strict';
+
+let pathToCommon;
 
 if (process.env.NODE_ENV === 'production') {
   pathToCommon = './transpiled-babel/index';
diff --git a/common/script/api-v3/errors.js b/common/script/api-v3/errors.js
index 5751a28c64..8c758051ab 100644
--- a/common/script/api-v3/errors.js
+++ b/common/script/api-v3/errors.js
@@ -1,6 +1,8 @@
+import extendableBuiltin from './libs/extendableBuiltin';
+
 // Base class for custom application errors
 // It extends Error and capture the stack trace
-export class CustomError extends Error {
+export class CustomError extends extendableBuiltin(Error) {
   constructor () {
     super();
     Error.captureStackTrace(this, this.constructor);
diff --git a/common/script/api-v3/libs/extendableBuiltin.js b/common/script/api-v3/libs/extendableBuiltin.js
new file mode 100644
index 0000000000..56186301c4
--- /dev/null
+++ b/common/script/api-v3/libs/extendableBuiltin.js
@@ -0,0 +1,11 @@
+// Babel 6 doesn't support extending native class (Error, Array, ...)
+// This function makes it possible to extend native classes with the same results as Babel 5
+module.exports = function extendableBuiltin (klass) {
+  function ExtendableBuiltin () {
+    klass.apply(this, arguments);
+  }
+  ExtendableBuiltin.prototype = Object.create(klass.prototype);
+  Object.setPrototypeOf(ExtendableBuiltin, klass);
+
+  return ExtendableBuiltin;
+};
diff --git a/common/script/api-v3/scoreTask.js b/common/script/api-v3/scoreTask.js
index f0244571f5..638e89a6a9 100644
--- a/common/script/api-v3/scoreTask.js
+++ b/common/script/api-v3/scoreTask.js
@@ -1,7 +1,7 @@
 import _ from 'lodash';
 import {
   NotAuthorized,
-} from '../../../website/src/libs/api-v3/errors';
+} from './errors';
 import i18n from '../i18n';
 
 const MAX_TASK_VALUE = 21.27;
diff --git a/common/script/index.js b/common/script/index.js
index a62bb72ef7..071a38da07 100644
--- a/common/script/index.js
+++ b/common/script/index.js
@@ -18,8 +18,17 @@ var $w, preenHistory, sortOrder,
 import content from './content/index';
 import i18n from './i18n';
 
+import * as errors from './api-v3/errors';
+import scoreTask from './api-v3/scoreTask';
+
 let api = module.exports = {};
 
+// Temporary location of API v3 files (soon to be removed)
+api.v3 = {
+  scoreTask,
+  errors,
+};
+
 api.i18n = i18n;
 api.shouldDo = shouldDo;
 
diff --git a/website/src/controllers/api-v3/tasks.js b/website/src/controllers/api-v3/tasks.js
index a58ac0a628..cfab73241c 100644
--- a/website/src/controllers/api-v3/tasks.js
+++ b/website/src/controllers/api-v3/tasks.js
@@ -10,13 +10,14 @@ import {
   NotAuthorized,
   BadRequest,
 } from '../../libs/api-v3/errors';
-import shared from '../../../../common';
+import common from '../../../../common';
 import Q from 'q';
 import _ from 'lodash';
 import moment from 'moment';
-import scoreTask from '../../../../common/script/api-v3/scoreTask';
 import { preenHistory } from '../../libs/api-v3/preening';
 
+const scoreTask = common.v3.scoreTask;
+
 let api = {};
 
 // challenge must be passed only when a challenge task is being created
@@ -334,8 +335,8 @@ api.updateTask = {
 
 function _generateWebhookTaskData (task, direction, delta, stats, user) {
   let extendedStats = _.extend(stats, {
-    toNextLevel: shared.tnl(user.stats.lvl),
-    maxHealth: shared.maxHealth,
+    toNextLevel: common.tnl(user.stats.lvl),
+    maxHealth: common.maxHealth,
     maxMP: user._statsComputed.maxMP, // TODO refactor as method not getter
   });
 
diff --git a/website/src/libs/api-v3/errors.js b/website/src/libs/api-v3/errors.js
index 884b65f102..10c87befdb 100644
--- a/website/src/libs/api-v3/errors.js
+++ b/website/src/libs/api-v3/errors.js
@@ -1,4 +1,6 @@
-import { CustomError } from '../../../../common/script/api-v3/errors';
+import common from '../../../../common/script';
+
+export const CustomError = common.v3.errors.CustomError;
 
 /**
  * @apiDefine NotAuthorized
@@ -11,7 +13,7 @@ import { CustomError } from '../../../../common/script/api-v3/errors';
  *       "message": "Not authorized."
  *     }
  */
-export { NotAuthorized } from '../../../../common/script/api-v3/errors';
+export const NotAuthorized = common.v3.errors.NotAuthorized;
 
 /**
  * @apiDefine BadRequest
@@ -24,7 +26,7 @@ export { NotAuthorized } from '../../../../common/script/api-v3/errors';
  *       "message": "Bad request."
  *     }
  */
-export { BadRequest } from '../../../../common/script/api-v3/errors';
+export const BadRequest = common.v3.errors.BadRequest;
 
 /**
  * @apiDefine NotFound
@@ -37,7 +39,7 @@ export { BadRequest } from '../../../../common/script/api-v3/errors';
  *       "message": "Not found."
  *     }
  */
-export { NotFound } from '../../../../common/script/api-v3/errors';
+export const NotFound = common.v3.errors.NotFound;
 
 /**
  * @apiDefine InternalServerError
diff --git a/website/src/middlewares/api-v3/cron.js b/website/src/middlewares/api-v3/cron.js
index 9b5042caf2..fecd6b05db 100644
--- a/website/src/middlewares/api-v3/cron.js
+++ b/website/src/middlewares/api-v3/cron.js
@@ -9,9 +9,10 @@ import Task from '../../models/task';
 import Q from 'q';
 import Group from '../../models/group';
 import User from '../../models/user';
-import scoreTask from '../../../../common/script/api-v3/scoreTask';
 import { preenUserHistory } from '../../libs/api-v3/preening';
 
+const scoreTask = common.v3.scoreTask;
+
 let clearBuffs = {
   str: 0,
   int: 0,
diff --git a/website/src/middlewares/api-v3/errorHandler.js b/website/src/middlewares/api-v3/errorHandler.js
index 65c1bd935d..95a592514d 100644
--- a/website/src/middlewares/api-v3/errorHandler.js
+++ b/website/src/middlewares/api-v3/errorHandler.js
@@ -1,8 +1,8 @@
 // The error handler middleware that handles all errors
 // and respond to the client
 import logger from '../../libs/api-v3/logger';
-import { CustomError } from '../../../../common/script/api-v3/errors';
 import {
+  CustomError,
   BadRequest,
   InternalServerError,
 } from '../../libs/api-v3/errors';