diff --git a/lib/types/validators/user-validators.js b/lib/types/validators/user-validators.js
index c396acc7b..240d57788 100644
--- a/lib/types/validators/user-validators.js
+++ b/lib/types/validators/user-validators.js
@@ -1,87 +1,87 @@
 // @flow
 
 import t, { type TInterface, type TUnion, type TEnums } from 'tcomb';
 
 import { policyTypeValidator } from '../../facts/policies.js';
 import { mixedRawThreadInfoValidator } from '../../permissions/minimally-encoded-raw-thread-info-validators.js';
-import { tShape, tID } from '../../utils/validation-utils.js';
+import { tShape, tID, tUserID } from '../../utils/validation-utils.js';
 import type {
   LogOutResponse,
   RegisterResponse,
   ServerLogInResponse,
   ClaimUsernameResponse,
 } from '../account-types.js';
 import {
   type ClientAvatar,
   clientAvatarValidator,
   type UpdateUserAvatarResponse,
 } from '../avatar-types.js';
 import { rawEntryInfoValidator } from '../entry-types.js';
 import {
   rawMessageInfoValidator,
   messageTruncationStatusesValidator,
 } from '../message-types.js';
 import {
   type SubscriptionUpdateResponse,
   threadSubscriptionValidator,
 } from '../subscription-types.js';
 import { createUpdatesResultValidator } from '../update-types.js';
 import {
   loggedOutUserInfoValidator,
   loggedInUserInfoValidator,
   userInfoValidator,
 } from '../user-types.js';
 
 export const registerResponseValidator: TInterface<RegisterResponse> =
   tShape<RegisterResponse>({
-    id: t.String,
+    id: tUserID,
     rawMessageInfos: t.list(rawMessageInfoValidator),
     currentUserInfo: loggedInUserInfoValidator,
     cookieChange: tShape({
       threadInfos: t.dict(tID, mixedRawThreadInfoValidator),
       userInfos: t.list(userInfoValidator),
     }),
   });
 
 export const logOutResponseValidator: TInterface<LogOutResponse> =
   tShape<LogOutResponse>({
     currentUserInfo: loggedOutUserInfoValidator,
   });
 
 export const logInResponseValidator: TInterface<ServerLogInResponse> =
   tShape<ServerLogInResponse>({
     currentUserInfo: loggedInUserInfoValidator,
     rawMessageInfos: t.list(rawMessageInfoValidator),
     truncationStatuses: messageTruncationStatusesValidator,
     userInfos: t.list(userInfoValidator),
     rawEntryInfos: t.maybe(t.list(rawEntryInfoValidator)),
     serverTime: t.Number,
     cookieChange: tShape({
       threadInfos: t.dict(tID, mixedRawThreadInfoValidator),
       userInfos: t.list(userInfoValidator),
     }),
     notAcknowledgedPolicies: t.maybe(t.list<TEnums>(policyTypeValidator)),
   });
 
 export const subscriptionUpdateResponseValidator: TInterface<SubscriptionUpdateResponse> =
   tShape<SubscriptionUpdateResponse>({
     threadSubscription: threadSubscriptionValidator,
   });
 
 export const updateUserAvatarResponseValidator: TInterface<UpdateUserAvatarResponse> =
   tShape<UpdateUserAvatarResponse>({
     updates: createUpdatesResultValidator,
   });
 
 export const updateUserAvatarResponderValidator: TUnion<
   ?ClientAvatar | UpdateUserAvatarResponse,
 > = t.union([
   t.maybe(clientAvatarValidator),
   updateUserAvatarResponseValidator,
 ]);
 
 export const claimUsernameResponseValidator: TInterface<ClaimUsernameResponse> =
   tShape<ClaimUsernameResponse>({
     message: t.String,
     signature: t.String,
   });