diff --git a/examples/aws-companion/server.cjs b/examples/aws-companion/server.cjs
index a0edb6b16..189cb0403 100644
--- a/examples/aws-companion/server.cjs
+++ b/examples/aws-companion/server.cjs
@@ -66,4 +66,9 @@ const server = app.listen(3020, () => {
   console.log('listening on port 3020')
 })
 
-companion.socket(server)
+// `setupSockets` (aliased as `companion.socket`) requires the same options
+// object passed to `companion.app(...)` since PR #6248 — it now derives the
+// external base path from `options.server` so WS URLs work behind reverse
+// proxies. Passing only `server` throws `Cannot read properties of undefined
+// (reading 'server')` inside getURLBuilder.
+companion.socket(server, options)
diff --git a/examples/companion/server/index.js b/examples/companion/server/index.js
index ab7c5f6ee..395b80890 100644
--- a/examples/companion/server/index.js
+++ b/examples/companion/server/index.js
@@ -71,7 +71,12 @@ app.use((err, req, res) => {
   res.status(500).json({ message: err.message, error: err })
 })
 
-companion.socket(app.listen(3020))
+// `companion.socket` requires the same options object passed to
+// `companion.app(...)` since PR #6248 — it derives the external base path
+// from `options.server` so WS URLs work behind reverse proxies. Omitting the
+// second arg throws "Cannot read properties of undefined (reading 'server')"
+// inside getURLBuilder.
+companion.socket(app.listen(3020), companionOptions)
 
 console.log('Welcome to Companion!')
 console.log(`Listening on http://0.0.0.0:${3020}`)
diff --git a/packages/@uppy/companion/README.md b/packages/@uppy/companion/README.md
index 30e37e963..eebdb77f9 100644
--- a/packages/@uppy/companion/README.md
+++ b/packages/@uppy/companion/README.md
@@ -68,7 +68,10 @@ on, you call the `socket` method like so.
 // ...
 const server = app.listen(PORT)
 
-companion.socket(server)
+// Pass the same `options` object you passed to `companion.app(options)` —
+// `companion.socket` needs `options.server` to compute the external base path
+// for incoming WS URLs (important behind reverse proxies).
+companion.socket(server, options)
 ```
 
 ### Run as standalone server