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
@@ -45,7 +45,7 @@
 });
 export type UserInfos = { +[id: string]: UserInfo };
 export const userInfosValidator: TDict<UserInfos> = t.dict(
-  t.String,
+  tUserID,
   userInfoValidator,
 );