diff --git a/testing/web-platform/tests/origin-isolation/insecure-http.sub.html b/testing/web-platform/tests/origin-isolation/insecure-http.sub.html
new file mode 100644
index 000000000000..04d4b2b63650
--- /dev/null
+++ b/testing/web-platform/tests/origin-isolation/insecure-http.sub.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Parent requests isolation, child requests isolation, child is a subdomain of the parent, but all over insecure HTTP</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<div id="log"></div>
+
+<script type="module">
+import { insertIframe, sendWasmModule, setBothDocumentDomains } from "./resources/helpers.mjs";
+
+let frameWindow;
+promise_setup(async () => {
+  frameWindow = await insertIframe("{{hosts[][www]}}", "?1");
+});
+
+// All isolation requests are ignored, since this is over insecure HTTP.
+// So both end up in the site-keyed agent cluster.
+
+promise_test(async () => {
+  const whatHappened = await sendWasmModule(frameWindow);
+
+  assert_equals(whatHappened, "WebAssembly.Module message received");
+}, "message event must occur");
+
+promise_test(async () => {
+  await setBothDocumentDomains(frameWindow);
+
+  // Must not throw
+  frameWindow.document;
+}, "setting document.domain must give sync access");
+</script>
diff --git a/testing/web-platform/tests/origin-isolation/insecure-http.sub.html.headers b/testing/web-platform/tests/origin-isolation/insecure-http.sub.html.headers
new file mode 100644
index 000000000000..ea3f6b335c76
--- /dev/null
+++ b/testing/web-platform/tests/origin-isolation/insecure-http.sub.html.headers
@@ -0,0 +1 @@
+Origin-Isolation: ?1
