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diff --git a/testing/web-platform/tests/html/semantics/embedded-content/the-iframe-element/content_document_changes_only_after_load_matures.html b/testing/web-platform/tests/html/semantics/embedded-content/the-iframe-element/content_document_changes_only_after_load_matures.html
new file mode 100644
index 0000000000..b657f26158
--- /dev/null
+++ b/testing/web-platform/tests/html/semantics/embedded-content/the-iframe-element/content_document_changes_only_after_load_matures.html
@@ -0,0 +1,28 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Iframe's contentDocument should only change after its pending load has matured.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body></body>
+<script>
+async_test(function(t) {
+    var iframe = document.createElement("iframe");
+    document.body.appendChild(iframe);
+    var checkedDuringParse = false;
+    iframe.onload = t.step_func_done(function() {
+        testContentDocument();
+        assert_true(checkedDuringParse);
+    });
+
+    let url = "support/iframe-that-checks-contentDocument.html";
+    window.testContentDocument = t.step_func(function() {
+        assert_true(iframe.contentDocument.location.toString().includes(url));
+        checkedDuringParse = true;
+    });
+
+    assert_equals(iframe.contentDocument.location.toString(), "about:blank");
+    iframe.src = url + "?pipe=trickle(d2)";
+    // The location of the contentDocument should not change until the new document has matured.
+    assert_equals(iframe.contentDocument.location.toString(), "about:blank");
+}, "contentDocument should only change after a load matures.");
+</script>