diff --git a/lib/permissions/special-roles.js b/lib/permissions/special-roles.js
--- a/lib/permissions/special-roles.js
+++ b/lib/permissions/special-roles.js
@@ -1,9 +1,18 @@
 // @flow
 
+import type { TRefinement } from 'tcomb';
+
+import { values } from '../utils/objects.js';
+import { tNumEnum } from '../utils/validation-utils.js';
+
 export const specialRoles = Object.freeze({
   DEFAULT_ROLE: 1,
   ADMIN_ROLE: 2,
 });
+export type SpecialRole = $Values<typeof specialRoles>;
+export const specialRoleValidator: TRefinement<number> = tNumEnum(
+  values(specialRoles),
+);
 
 export const defaultSpecialRoles = Object.freeze({
   Members: specialRoles.DEFAULT_ROLE,
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
@@ -35,6 +35,10 @@
 import { type ThreadType, threadTypeValidator } from './thread-types-enum.js';
 import type { ClientUpdateInfo, ServerUpdateInfo } from './update-types.js';
 import type { UserInfo, UserInfos } from './user-types.js';
+import {
+  specialRoleValidator,
+  type SpecialRole,
+} from '../permissions/special-roles.js';
 import {
   type ThreadEntity,
   threadEntityValidator,
@@ -77,6 +81,7 @@
   +name: string,
   +permissions: ThreadRolePermissionsBlob,
   +isDefault: boolean,
+  +specialRole?: ?SpecialRole,
 };
 export const legacyRoleInfoValidator: TInterface<LegacyRoleInfo> =
   tShape<LegacyRoleInfo>({
@@ -84,6 +89,7 @@
     name: t.String,
     permissions: threadRolePermissionsBlobValidator,
     isDefault: t.Boolean,
+    specialRole: t.maybe(specialRoleValidator),
   });
 
 export type RoleInfo = LegacyRoleInfo | MinimallyEncodedRoleInfo;