diff --git a/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.html b/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.html
index a0e70a524a..06dc851ef1 100644
--- a/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.html
+++ b/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.html
@@ -7,7 +7,7 @@
         window.parseTimeDclFired = true;
       });
     </script>
-    <script async src="/assets/parse_time_async.js"></script>
+    <script async src="/assets/parse_time_async_chunked.js"></script>
   </head>
   <body>
     <!--
diff --git a/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.js b/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.js
new file mode 100644
index 0000000000..2b7172b276
--- /dev/null
+++ b/moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.js
@@ -0,0 +1,4 @@
+window.parseTimeAsyncSawTail = !!document.getElementById("late");
+window.parseTimeAsyncSawDcl = window.parseTimeDclFired === true;
+// Release the response tail only after observing the parser's partial DOM.
+void fetch("/compat/parse-time-async-classic-chunked-executed");
diff --git a/moli-test-support/src/lib.rs b/moli-test-support/src/lib.rs
index 6cb26618a8..c05112a3b3 100644
--- a/moli-test-support/src/lib.rs
+++ b/moli-test-support/src/lib.rs
@@ -650,6 +650,8 @@ const PARSE_TIME_ASYNC_CLASSIC_HTML: &str =
     include_str!("../../moli-core/tests/fixtures/runtime/parse_time_async_classic.html");
 const PARSE_TIME_ASYNC_CLASSIC_CHUNKED_HTML: &str =
     include_str!("../../moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.html");
+const PARSE_TIME_ASYNC_CLASSIC_CHUNKED_JS: &str =
+    include_str!("../../moli-core/tests/fixtures/runtime/parse_time_async_classic_chunked.js");
 const PARSE_TIME_ASYNC_CLASSIC_SLOW_CHUNKED_TAIL_HTML: &str = include_str!(
     "../../moli-core/tests/fixtures/runtime/parse_time_async_classic_slow_chunked_tail.html"
 );
diff --git a/moli-test-support/src/routes_core.rs b/moli-test-support/src/routes_core.rs
index 480e045c33..0b0bd16957 100644
--- a/moli-test-support/src/routes_core.rs
+++ b/moli-test-support/src/routes_core.rs
@@ -2096,8 +2096,11 @@ pub(super) async fn parse_time_async_classic_chunked_page(headers: HeaderMap) ->
         {
             return;
         }
-        let _ = tokio::time::timeout(Duration::from_millis(500), tail_gate.notified()).await;
-        sleep(Duration::from_millis(20)).await;
+        // A request for the asset does not imply that its body has arrived or
+        // executed. Its dedicated script acknowledges execution before tail
+        // delivery. The timeout is only a bounded failure escape: the test's
+        // before-tail assertions still fail if the parser cannot make progress.
+        let _ = tokio::time::timeout(Duration::from_secs(5), tail_gate.notified()).await;
         let _ = tx
             .send(Ok::<Bytes, std::convert::Infallible>(Bytes::from(tail)))
             .await;
@@ -2114,6 +2117,13 @@ pub(super) async fn parse_time_async_classic_chunked_page(headers: HeaderMap) ->
         .expect("chunked async classic response should build")
 }
 
+pub(super) async fn parse_time_async_classic_chunked_executed(headers: HeaderMap) -> StatusCode {
+    if let Some(host_key) = request_host_key(&headers) {
+        notify_parse_time_async_chunked_tail_gate_if_present(&host_key);
+    }
+    StatusCode::NO_CONTENT
+}
+
 pub(super) async fn parse_time_async_classic_slow_chunked_tail_page() -> Response {
     let split_marker = "<script defer";
     let split_index = PARSE_TIME_ASYNC_CLASSIC_SLOW_CHUNKED_TAIL_HTML
@@ -4362,13 +4372,14 @@ pub(super) async fn asset_parse_time_defer_script() -> Response {
     javascript_response(PARSE_TIME_DEFER_JS)
 }
 
-pub(super) async fn asset_parse_time_async_script(headers: HeaderMap) -> Response {
-    if let Some(host_key) = request_host_key(&headers) {
-        notify_parse_time_async_chunked_tail_gate_if_present(&host_key);
-    }
+pub(super) async fn asset_parse_time_async_script() -> Response {
     javascript_response(PARSE_TIME_ASYNC_JS)
 }
 
+pub(super) async fn asset_parse_time_async_chunked_script() -> Response {
+    javascript_response(PARSE_TIME_ASYNC_CLASSIC_CHUNKED_JS)
+}
+
 pub(super) async fn asset_parse_time_async_load_order_script() -> Response {
     javascript_response(PARSE_TIME_ASYNC_LOAD_ORDER_JS)
 }
diff --git a/moli-test-support/src/server_routes.rs b/moli-test-support/src/server_routes.rs
index 46959608b7..7a6c387c78 100644
--- a/moli-test-support/src/server_routes.rs
+++ b/moli-test-support/src/server_routes.rs
@@ -1129,6 +1129,10 @@ pub(super) fn build_router() -> Router {
             "/compat/parse-time-async-classic-chunked",
             get(parse_time_async_classic_chunked_page),
         )
+        .route(
+            "/compat/parse-time-async-classic-chunked-executed",
+            get(parse_time_async_classic_chunked_executed),
+        )
         .route(
             "/compat/parse-time-async-classic-slow-chunked-tail",
             get(parse_time_async_classic_slow_chunked_tail_page),
@@ -2138,6 +2142,10 @@ pub(super) fn build_router() -> Router {
             "/assets/parse_time_async.js",
             get(asset_parse_time_async_script),
         )
+        .route(
+            "/assets/parse_time_async_chunked.js",
+            get(asset_parse_time_async_chunked_script),
+        )
         .route(
             "/assets/parse_time_async_load_order.js",
             get(asset_parse_time_async_load_order_script),