diff --git a/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/reload.window.js b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/reload.window.js
new file mode 100644
index 00000000000000..d6ff9dc7a45425
--- /dev/null
+++ b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/reload.window.js
@@ -0,0 +1,71 @@
+// This test tests for the nonexistence of a reload override buffer, which is
+// used in a previous version of the HTML Standard to make reloads of a
+// document.open()'d document load the written-to document rather than doing an
+// actual reload of the document's URL.
+//
+// This test has a somewhat interesting structure compared to the other tests
+// in this directory. It eschews the <iframe> structure used by other tests,
+// since when the child frame is reloaded it would adopt the URL of the test
+// page (the responsible document of the entry settings object), and the spec
+// forbids navigation in nested browsing contexts to the same URL as their
+// parent. To work around that, we use window.open() which does not suffer from
+// that restriction.
+//
+// In any case, this test as the caller of `document.open()` would be used both
+// as the test file and as part of the test file. The `if (!opener)` condition
+// controls what role this file plays.
+
+if (!opener) {
+  async_test(t => {
+    const testURL = document.URL;
+    const dummyURL = new URL("resources/dummy.html", document.URL).href;
+
+    // 1. Open an auxiliary window.
+    const win = window.open("resources/dummy.html");
+    t.add_cleanup(() => { win.close(); });
+
+    win.addEventListener("load", t.step_func(() => {
+      // The timeout seems to be necessary for Firefox, which when `load` is
+      // called may still have an active parser.
+      t.step_timeout(() => {
+        const doc = win.document;
+        assert_true(doc.body.textContent.includes("Dummy"), "precondition");
+        assert_equals(doc.URL, dummyURL, "precondition");
+
+        window.onChildLoad = t.step_func(message => {
+          // 3. The dynamically overwritten content will trigger this function,
+          // which puts in place the actual test.
+
+          assert_equals(message, "Written", "script on written page is executed");
+          assert_true(win.document.body.textContent.includes("Content"), "page is written to");
+          assert_equals(win.document.URL, testURL, "postcondition: after document.write()");
+          assert_equals(win.document, doc, "document.open should not change the document object");
+          window.onChildLoad = t.step_func_done(message => {
+            // 6. This function should be called from the if (opener) branch of
+            // this file. It would throw an assertion error if the overwritten
+            // content was executed instead.
+            assert_equals(message, "Done!", "actual test");
+            assert_true(win.document.body.textContent.includes("Back to the test"), "test is reloaded");
+            assert_equals(win.document.URL, testURL, "postcondition: after reload");
+            assert_not_equals(win.document, doc, "reload should change the document object");
+          });
+
+          // 4. Reload the pop-up window. Because of the doc.open() call, this
+          // pop-up window will reload to the same URL as this test itself.
+          win.location.reload();
+        });
+
+        // 2. When it is loaded, dynamically overwrite its content.
+        assert_equals(doc.open(), doc);
+        assert_equals(doc.URL, testURL, "postcondition: after document.open()");
+        doc.write("<p>Content</p><script>opener.onChildLoad('Written');</script>");
+        doc.close();
+      }, 100);
+    }), { once: true });
+  }, "Reloading a document.open()'d page should reload the URL of the entry realm's responsible document");
+} else {
+  document.write("<p>Back to the test</p>");
+  // 5. Since this window is window.open()'d, opener refers to the test window.
+  // Inform the opener that reload succeeded.
+  opener.onChildLoad("Done!");
+}
diff --git a/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/dummy.html b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/dummy.html
new file mode 100644
index 00000000000000..a092f4e2d7e6d5
--- /dev/null
+++ b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/dummy.html
@@ -0,0 +1,2 @@
+<!-- Like /common/blank.html, but with some content in it. -->
+<p>Dummy</p>