diff --git a/lib/utils/user-info-extraction-utils.js b/lib/utils/user-info-extraction-utils.js
index 5d80af0b0..288e74a16 100644
--- a/lib/utils/user-info-extraction-utils.js
+++ b/lib/utils/user-info-extraction-utils.js
@@ -1,83 +1,85 @@
 // @flow
 
 import _memoize from 'lodash/memoize.js';
 import t, { type TType, type TInterface } from 'tcomb';
 
 import type { CallSingleKeyserverEndpointResponse } from '../keyserver-conn/call-single-keyserver-endpoint.js';
 import { mixedRawThreadInfoValidator } from '../permissions/minimally-encoded-raw-thread-info-validators.js';
 import type { Endpoint } from '../types/endpoints.js';
 import type { MixedRawThreadInfos } from '../types/thread-types.js';
 import { userInfoValidator } from '../types/user-types.js';
 import type { UserInfo } from '../types/user-types.js';
 import { endpointValidators } from '../types/validators/endpoint-validators.js';
 import { extractUserIDsFromPayload } from '../utils/conversion-utils.js';
 import { tID, tShape } from '../utils/validation-utils.js';
 
 type AdditionalCookieChange = {
   +threadInfos: MixedRawThreadInfos,
   +userInfos: $ReadOnlyArray<UserInfo>,
   +cookieInvalidated?: boolean,
   sessionID?: string,
   cookie?: string,
 };
 
 type AdditionalResponseFields = {
   +cookieChange: AdditionalCookieChange,
   +error?: string,
   +payload?: Object,
   +success: boolean,
 };
 
 const additionalResponseFieldsValidator = tShape<AdditionalResponseFields>({
   cookieChange: t.maybe(
     tShape<AdditionalCookieChange>({
       threadInfos: t.dict(tID, mixedRawThreadInfoValidator),
       userInfos: t.list(userInfoValidator),
       cookieInvalidated: t.maybe(t.Boolean),
       sessionID: t.maybe(t.String),
       cookie: t.maybe(t.String),
     }),
   ),
   error: t.maybe(t.String),
   payload: t.maybe(t.Object),
   success: t.maybe(t.Boolean),
 });
 
 function extendResponderValidatorBase<T>(inputValidator: TType<T>): TType<T> {
   if (inputValidator.meta.kind === 'union') {
     const newTypes = [];
     for (const innerValidator of inputValidator.meta.types) {
       const newInnerValidator = extendResponderValidatorBase(innerValidator);
       newTypes.push(newInnerValidator);
     }
     return t.union(newTypes);
   } else if (inputValidator.meta.kind === 'interface') {
     const recastValidator: TInterface<Object> = (inputValidator: any);
 
     return (tShape({
       ...recastValidator.meta.props,
       ...additionalResponseFieldsValidator.meta.props,
     }): any);
   } else if (inputValidator.meta.kind === 'maybe') {
     const typeObj = extendResponderValidatorBase(inputValidator.meta.type);
     return (t.maybe(typeObj): any);
+  } else if (inputValidator.meta.kind === 'subtype') {
+    return extendResponderValidatorBase(inputValidator.meta.type);
   }
 
   return inputValidator;
 }
 
 const extendResponderValidator = _memoize(extendResponderValidatorBase);
 
 function extractAndPersistUserInfosFromEndpointResponse(
   message: CallSingleKeyserverEndpointResponse,
   endpoint: Endpoint,
 ): void {
   const extendedValidator = extendResponderValidator(
     endpointValidators[endpoint].validator,
   );
   // eslint-disable-next-line no-unused-vars
   const newUserIDs = extractUserIDsFromPayload(extendedValidator, message);
   // TODO: dispatch an action adding the new user ids to the UserStore
 }
 
 export { extractAndPersistUserInfosFromEndpointResponse };