diff --git a/testing/web-platform/tests/portals/portals-host-exposure.sub.html b/testing/web-platform/tests/portals/portals-host-exposure.sub.html
new file mode 100644
index 000000000000..83e31bd47351
--- /dev/null
+++ b/testing/web-platform/tests/portals/portals-host-exposure.sub.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<script>
+  let channelIndex = 0;
+  async function openPortalAndReceiveMessage(portalSrc) {
+    let channelName = `portals-host-exposure-${channelIndex++}`
+    let broadcastChannel = new BroadcastChannel(channelName);
+    try {
+      let received = new Promise((resolve, reject) => {
+        broadcastChannel.addEventListener('message', e => {
+          resolve(e.data);
+        }, {once: true})
+      });
+      let portal = document.createElement('portal');
+      portal.src = `${portalSrc}?broadcastchannel=${channelName}`;
+      document.body.appendChild(portal);
+      return await received;
+    } finally {
+      broadcastChannel.close();
+    }
+  }
+
+  promise_test(async t => {
+    let {hasHost} = await openPortalAndReceiveMessage(
+        'resources/portal-host.html');
+    assert_true(hasHost, "window.portalHost should be defined");
+  }, "window.portalHost should be exposed in same-origin portal");
+
+  promise_test(async t => {
+    let {hasHost} = await openPortalAndReceiveMessage(
+        'http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/portal-host-cross-origin.sub.html');
+    assert_true(hasHost, "window.portalHost should be defined");
+  }, "window.portalHost should be exposed in cross-origin portal");
+
+  promise_test(async t => {
+    let {hasHost} = await openPortalAndReceiveMessage(
+        'resources/portal-host-cross-origin-navigate.sub.html');
+    assert_true(hasHost, "window.portalHost should be defined");
+  }, "window.portalHost should be exposed in portal after cross-origin navigation");
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html b/testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html
new file mode 100644
index 000000000000..44c6c16c5771
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-cross-origin-navigate.sub.html
@@ -0,0 +1,7 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    let channelName = new URL(location).searchParams.get('broadcastchannel');
+    window.location.href = `http://{{hosts[alt][www]}}:{{ports[http][0]}}/portals/resources/portal-host-cross-origin.sub.html?broadcastchannel=${channelName}`;
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-host-cross-origin.sub.html b/testing/web-platform/tests/portals/resources/portal-host-cross-origin.sub.html
new file mode 100644
index 000000000000..dc4e9e7b5de4
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host-cross-origin.sub.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    let forwardingIframe = document.createElement('iframe');
+    let channelName = new URL(location).searchParams.get('broadcastchannel');
+    forwardingIframe.src = `http://{{host}}:{{ports[http][0]}}/portals/resources/portal-forward-with-broadcast.html?broadcastchannel=${channelName}`;
+    forwardingIframe.onload = () => {
+      let message = {
+        hasHost: !!window.portalHost
+      };
+      forwardingIframe.contentWindow.postMessage(message, '*');
+    }
+    document.body.appendChild(forwardingIframe);
+  </script>
+</body>
diff --git a/testing/web-platform/tests/portals/resources/portal-host.html b/testing/web-platform/tests/portals/resources/portal-host.html
new file mode 100644
index 000000000000..5043a158ea74
--- /dev/null
+++ b/testing/web-platform/tests/portals/resources/portal-host.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<body>
+  <script>
+    let message = {
+      hasHost: !!window.portalHost
+    };
+    let broadcastChannel = new BroadcastChannel(new URL(location).searchParams.get('broadcastchannel'));
+    try {
+      broadcastChannel.postMessage(message);
+    } finally {
+      broadcastChannel.close();
+    }
+  </script>
+</body>
