diff --git a/docs/manual/deploy.md b/docs/manual/deploy.md
index a46afc7a8..ffa1d152d 100644
--- a/docs/manual/deploy.md
+++ b/docs/manual/deploy.md
@@ -927,6 +927,14 @@ does not.  See the
 [*`WorkersD1KvStore`*](./kv.md#workersd1kvstore-cloudflare-workers-only)
 section for details.
 
+> [!WARNING]
+> Do not use `InProcessMessageQueue` on Cloudflare Workers.  A delayed
+> enqueue depends on `setTimeout()`, which may never run after the isolate
+> exits, and `listen()` polls memory that is not guaranteed to survive or
+> be shared across requests.  Use `WorkersMessageQueue` and a `queue()`
+> handler, as shown in [Manual queue processing](#manual-queue-processing),
+> or configure another durable queue.
+
 #### Node.js compatibility
 
 Fedify depends on Node.js APIs for cryptography and DNS, so Workers need
diff --git a/docs/manual/mq.md b/docs/manual/mq.md
index 1a6498fda..b75dd22bf 100644
--- a/docs/manual/mq.md
+++ b/docs/manual/mq.md
@@ -44,6 +44,17 @@ Cons
 :   Not suitable for production, doesn't persist messages between restarts,
     no native retry mechanism.
 
+> [!WARNING]
+> `InProcessMessageQueue` cannot run on [Cloudflare Workers].  A delayed
+> `enqueue()` schedules a `setTimeout()` and resolves immediately, but a
+> Worker isolate can terminate after the response, so the timer may never
+> run and the message may never enter the queue.  `listen()` only polls
+> in-memory state, which is not guaranteed to survive or be shared across
+> requests.  Use
+> [`WorkersMessageQueue`](#workersmessagequeue-cloudflare-workers-only) with
+> a `queue()` handler, or another durable queue.  Do not treat a delayed
+> enqueue as reliable on Workers.
+
 ~~~~ typescript twoslash
 import type { KvStore } from "@fedify/fedify";
 // ---cut-before---