diff --git a/testing/web-platform/tests/navigation-api/navigation-methods/navigate-relative-url-utf8.html b/testing/web-platform/tests/navigation-api/navigation-methods/navigate-relative-url-utf8.html
new file mode 100644
index 0000000000000..22c723fd3bc28
--- /dev/null
+++ b/testing/web-platform/tests/navigation-api/navigation-methods/navigate-relative-url-utf8.html
@@ -0,0 +1,23 @@
+<!doctype html>
+<meta charset={{GET[encoding]}}> <!-- ends up as <meta charset> by default which is windows-1252 -->
+<meta name=variant content="?encoding=windows-1252">
+<meta name=variant content="?encoding=x-cp1251">
+<meta name=variant content="?encoding=utf8">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<iframe id="i" src="/common/blank.html"></iframe>
+<!-- Test for https://github.com/whatwg/html/pull/9756 -->
+
+<script>
+async_test(t => {
+  window.onload = t.step_func(() => {
+    i.contentWindow.navigation.navigate("?\u00FF");
+
+    i.onload = t.step_func_done(() => {
+      const iframeURL = new URL(i.contentWindow.navigation.currentEntry.url);
+      assert_equals(iframeURL.pathname, "/common/blank.html", "pathname");
+      assert_equals(iframeURL.search, "?%C3%BF", "search");
+    });
+  });
+}, "navigate() should resolve URLs assuming UTF-8, ignoring the document's encoding");
+</script>
