diff --git a/lib/api/2fa/u2f.js b/lib/api/2fa/u2f.js
index d73f1112..0076549b 100644
--- a/lib/api/2fa/u2f.js
+++ b/lib/api/2fa/u2f.js
@@ -3,12 +3,21 @@
 const Joi = require('joi');
 const ObjectID = require('mongodb').ObjectID;
 
-const U2F_ERRORS = new Map([
-    [1, 'Unknown error'],
-    [2, 'Bad request'],
-    [3, 'Client configuration is not supported'],
-    [4, 'The presented device is not eligible for this request'],
-    [5, 'Timeout reached while waiting for key']
+const U2F_ERROR_CODES = {
+    OK: 0,
+    OTHER_ERROR: 1,
+    BAD_REQUEST: 2,
+    CONFIGURATION_UNSUPPORTED: 3,
+    DEVICE_INELIGIBLE: 4,
+    TIMEOUT: 5
+};
+
+const U2F_ERROR_MESSAGES = new Map([
+    [U2F_ERROR_CODES.OTHER_ERROR, 'Unknown error'],
+    [U2F_ERROR_CODES.BAD_REQUEST, 'Bad request'],
+    [U2F_ERROR_CODES.CONFIGURATION_UNSUPPORTED, 'Client configuration is not supported'],
+    [U2F_ERROR_CODES.DEVICE_INELIGIBLE, 'The presented device is not eligible for this request'],
+    [U2F_ERROR_CODES.TIMEOUT, 'Timeout reached while waiting for key']
 ]);
 
 module.exports = (db, server, userHandler) => {
@@ -57,17 +66,6 @@ module.exports = (db, server, userHandler) => {
             return next();
         });
     });
-    /*
-var t = {
-    registrationData:
-        'BQSp4XE8GaJNIHEpWRa6sVkKeIcCqr2ODhi9FL9b4ac70ttiKH9I4rK6Y7eV9HVFQX78T_YyYhXL89__bZxmjX4TQJQZHupSA74vy9WPHjnBA69G1tfLfjQ4nFxiscGneMh2PTBzPjUyKBlHJkg_WJtVCThL2Lbc5WQ8ziU37c52uLEwggJEMIIBLqADAgECAgRVYr6gMAsGCSqGSIb3DQEBCzAuMSwwKgYDVQQDEyNZdWJpY28gVTJGIFJvb3QgQ0EgU2VyaWFsIDQ1NzIwMDYzMTAgFw0xNDA4MDEwMDAwMDBaGA8yMDUwMDkwNDAwMDAwMFowKjEoMCYGA1UEAwwfWXViaWNvIFUyRiBFRSBTZXJpYWwgMTQzMjUzNDY4ODBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABEszH3c9gUS5mVy-RYVRfhdYOqR2I2lcvoWsSCyAGfLJuUZ64EWw5m8TGy6jJDyR_aYC4xjz_F2NKnq65yvRQwmjOzA5MCIGCSsGAQQBgsQKAgQVMS4zLjYuMS40LjEuNDE0ODIuMS41MBMGCysGAQQBguUcAgEBBAQDAgUgMAsGCSqGSIb3DQEBCwOCAQEArBbZs262s6m3bXWUs09Z9Pc-28n96yk162tFHKv0HSXT5xYU10cmBMpypXjjI-23YARoXwXn0bm-BdtulED6xc_JMqbK-uhSmXcu2wJ4ICA81BQdPutvaizpnjlXgDJjq6uNbsSAp98IStLLp7fW13yUw-vAsWb5YFfK9f46Yx6iakM3YqNvvs9M9EUJYl_VrxBJqnyLx2iaZlnpr13o8NcsKIJRdMUOBqt_ageQg3ttsyq_3LyoNcu7CQ7x8NmeCGm_6eVnZMQjDmwFdymwEN4OxfnM5MkcKCYhjqgIGruWkVHsFnJa8qjZXneVvKoiepuUQyDEJ2GcqvhU2YKY1zBEAiBKahEVX1Kw2X6rL1kKeskPU-fNqwqLo5S1ylHDcesRpgIgPNg0uHVswZquH6YLfUSNUKg_bYBGXOxHKWH5qNl2bB4',
-    version: 'U2F_V2',
-    challenge: '2kbypDmNIkM6-oaVKjB7ZN1J1jiyzoU8WxLGX8yVUpY',
-    clientData:
-        'eyJ0eXAiOiJuYXZpZ2F0b3IuaWQuZmluaXNoRW5yb2xsbWVudCIsImNoYWxsZW5nZSI6IjJrYnlwRG1OSWtNNi1vYVZLakI3Wk4xSjFqaXl6b1U4V3hMR1g4eVZVcFkiLCJvcmlnaW4iOiJodHRwczovL2xvY2FsaG9zdDozMDAwIiwiY2lkX3B1YmtleSI6InVudXNlZCJ9'
-};
-
- */
 
     // Send response from U2F key
     server.post('/users/:user/2fa/u2f/enable', (req, res, next) => {
@@ -109,9 +107,20 @@ var t = {
         }
 
         if (result.value.errorCode) {
+            let error;
+
+            switch (result.value.errorCode) {
+                case U2F_ERROR_CODES.DEVICE_INELIGIBLE:
+                    error = 'U2F token is already registered';
+                    break;
+                default:
+                    error = U2F_ERROR_MESSAGES.get(result.value.errorCode) || 'Unknown error code' + result.value.errorCode;
+            }
+
             res.json({
-                error: U2F_ERRORS.get(result.value.errorCode) || 'Unknown error'
+                error
             });
+
             return next();
         }
 
@@ -285,9 +294,20 @@ var t = {
         }
 
         if (result.value.errorCode) {
+            let error;
+
+            switch (result.value.errorCode) {
+                case U2F_ERROR_CODES.DEVICE_INELIGIBLE:
+                    error = 'U2F token is not registered';
+                    break;
+                default:
+                    error = U2F_ERROR_MESSAGES.get(result.value.errorCode) || 'Unknown error code' + result.value.errorCode;
+            }
+
             res.json({
-                error: U2F_ERRORS.get(result.value.errorCode) || 'Unknown error'
+                error
             });
+
             return next();
         }