diff --git a/crates/buzz-relay/src/api/typing_postgres_tests.rs b/crates/buzz-relay/src/api/typing_postgres_tests.rs
index 3883a92e19..9e9c700957 100644
--- a/crates/buzz-relay/src/api/typing_postgres_tests.rs
+++ b/crates/buzz-relay/src/api/typing_postgres_tests.rs
@@ -202,3 +202,22 @@ async fn typing_without_channel_is_rejected() {
         "{body}"
     );
 }
+
+#[tokio::test]
+#[ignore = "requires Postgres and Redis"]
+async fn oversized_typing_is_rejected() {
+    let f = Fixture::new().await;
+    let event = EventBuilder::new(Kind::Custom(20002), "x".repeat(2048))
+        .tags([Tag::parse(["h".to_string(), f.channel.to_string()]).unwrap()])
+        .sign_with_keys(&f.member)
+        .unwrap();
+    let (status, body) = f.post(&f.member, &event).await;
+    assert_eq!(status, axum::http::StatusCode::BAD_REQUEST, "{body}");
+    assert!(
+        body["error"]
+            .as_str()
+            .unwrap_or_default()
+            .contains("too large"),
+        "{body}"
+    );
+}
diff --git a/crates/buzz-relay/src/handlers/event.rs b/crates/buzz-relay/src/handlers/event.rs
index 8dd05e5245..f6cbe7af7a 100644
--- a/crates/buzz-relay/src/handlers/event.rs
+++ b/crates/buzz-relay/src/handlers/event.rs
@@ -1056,6 +1056,12 @@ async fn publish_channel_ephemeral(
     Ok(())
 }
 
+/// Upper bound on content plus tag values for an HTTP typing indicator.
+/// Real indicators carry empty content and at most three short tags (`h`,
+/// root `e`, reply `e`, roughly 250 bytes). Without a cap a member could post
+/// up to the HTTP body limit and have it fanned out to every subscriber.
+const MAX_HTTP_TYPING_BYTES: usize = 1024;
+
 /// Publishes a typing indicator (kind:20002) submitted through HTTP
 /// `POST /events`, for clients that sign but hold no WebSocket, such as
 /// app-hosted agents. Applies the gates the WebSocket path applies to
@@ -1075,6 +1081,18 @@ pub(crate) async fn publish_http_typing(
     let ch_id = super::ingest::extract_channel_id(&event).ok_or_else(|| {
         IngestError::Rejected("invalid: typing indicator needs a channel UUID h tag".into())
     })?;
+    let size = event.content.len()
+        + event
+            .tags
+            .iter()
+            .flat_map(|tag| tag.as_slice())
+            .map(String::len)
+            .sum::<usize>();
+    if size > MAX_HTTP_TYPING_BYTES {
+        return Err(IngestError::Rejected(format!(
+            "invalid: typing indicator too large (max {MAX_HTTP_TYPING_BYTES} bytes of content and tags)"
+        )));
+    }
     let event_clone = event.clone();
     match tokio::task::spawn_blocking(move || verify_event(&event_clone)).await {
         Ok(Ok(())) => {}