diff --git a/lib/shared/updates/delete-account-spec.js b/lib/shared/updates/delete-account-spec.js
--- a/lib/shared/updates/delete-account-spec.js
+++ b/lib/shared/updates/delete-account-spec.js
@@ -11,7 +11,7 @@
   AccountDeletionUpdateInfo,
 } from '../../types/update-types.js';
 import type { UserInfos } from '../../types/user-types.js';
-import { tNumber, tShape } from '../../utils/validation-utils.js';
+import { tNumber, tShape, tUserID } from '../../utils/validation-utils.js';
 
 export const deleteAccountSpec: UpdateSpec<
   AccountDeletionUpdateInfo,
@@ -98,6 +98,6 @@
     type: tNumber(updateTypes.DELETE_ACCOUNT),
     id: t.String,
     time: t.Number,
-    deletedUserID: t.String,
+    deletedUserID: tUserID,
   }),
 });
diff --git a/lib/shared/updates/update-user-spec.js b/lib/shared/updates/update-user-spec.js
--- a/lib/shared/updates/update-user-spec.js
+++ b/lib/shared/updates/update-user-spec.js
@@ -9,7 +9,7 @@
   UserRawUpdateInfo,
   UserUpdateData,
 } from '../../types/update-types.js';
-import { tNumber, tShape } from '../../utils/validation-utils.js';
+import { tNumber, tShape, tUserID } from '../../utils/validation-utils.js';
 
 export const updateUserSpec: UpdateSpec<
   UserUpdateInfo,
@@ -62,6 +62,6 @@
     type: tNumber(updateTypes.UPDATE_USER),
     id: t.String,
     time: t.Number,
-    updatedUserID: t.String,
+    updatedUserID: tUserID,
   }),
 });
diff --git a/lib/types/thread-types.js b/lib/types/thread-types.js
--- a/lib/types/thread-types.js
+++ b/lib/types/thread-types.js
@@ -35,7 +35,7 @@
 import type { UserInfo, UserInfos } from './user-types.js';
 import type { SpecialRole } from '../permissions/special-roles.js';
 import { type ThreadEntity } from '../utils/entity-text.js';
-import { tID, tShape } from '../utils/validation-utils.js';
+import { tID, tShape, tUserID } from '../utils/validation-utils.js';
 
 export type LegacyMemberInfo = {
   +id: string,
@@ -45,7 +45,7 @@
 };
 export const legacyMemberInfoValidator: TInterface<LegacyMemberInfo> =
   tShape<LegacyMemberInfo>({
-    id: t.String,
+    id: tUserID,
     role: t.maybe(tID),
     permissions: threadPermissionsInfoValidator,
     isSender: t.Boolean,
diff --git a/lib/types/user-types.js b/lib/types/user-types.js
--- a/lib/types/user-types.js
+++ b/lib/types/user-types.js
@@ -38,7 +38,7 @@
   +avatar?: ?ClientAvatar,
 };
 export const userInfoValidator: TInterface<UserInfo> = tShape<UserInfo>({
-  id: t.String,
+  id: tUserID,
   username: t.maybe(t.String),
   relationshipStatus: t.maybe(userRelationshipStatusValidator),
   avatar: t.maybe(clientAvatarValidator),
@@ -82,7 +82,7 @@
 };
 export const loggedInUserInfoValidator: TInterface<LoggedInUserInfo> =
   tShape<LoggedInUserInfo>({
-    id: t.String,
+    id: tUserID,
     username: t.String,
     settings: t.maybe(defaultNotificationPayloadValidator),
     avatar: t.maybe(clientAvatarValidator),