diff --git a/frontend-pwa/src/api/client.ts b/frontend-pwa/src/api/client.ts
index 5f44d82a1..b0eca26ab 100644
--- a/frontend-pwa/src/api/client.ts
+++ b/frontend-pwa/src/api/client.ts
@@ -4,12 +4,17 @@
 import { z } from 'zod';
 import { customFetchParsed } from './fetcher';
 
+export type UserId = string & { readonly brand: 'UserId' };
+
+export interface User {
+  id: UserId;
+  display_name: string;
+}
+
 const userSchema = z.object({
-  id: z.string(),
+  id: z.string().transform(id => id as UserId),
   display_name: z.string(),
-});
-
-export type User = z.infer<typeof userSchema>;
+}) satisfies z.ZodType<User>;
 
 export const listUsers = (signal?: AbortSignal) =>
   customFetchParsed('/api/users', z.array(userSchema), { signal });