diff --git a/testing/web-platform/meta/MANIFEST.json b/testing/web-platform/meta/MANIFEST.json
index 3c8ba36729fc0..3e03cd84db33f 100644
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -337417,6 +337417,12 @@
      {}
     ]
    ],
+   "html/semantics/forms/form-submission-0/constructing-form-data-set.html": [
+    [
+     "/html/semantics/forms/form-submission-0/constructing-form-data-set.html",
+     {}
+    ]
+   ],
    "html/semantics/forms/form-submission-0/form-data-set-usv.html": [
     [
      "/html/semantics/forms/form-submission-0/form-data-set-usv.html",
@@ -574106,6 +574112,10 @@
    "da39a3ee5e6b4b0d3255bfef95601890afd80709",
    "support"
   ],
+  "html/semantics/forms/form-submission-0/constructing-form-data-set.html": [
+   "28ddddb0e685b6de4bb1270afdd791865d6bb787",
+   "testharness"
+  ],
   "html/semantics/forms/form-submission-0/contains.json": [
    "5cb7e225df89561a1137933615b93c9912444006",
    "support"
diff --git a/testing/web-platform/tests/html/semantics/forms/form-submission-0/constructing-form-data-set.html b/testing/web-platform/tests/html/semantics/forms/form-submission-0/constructing-form-data-set.html
new file mode 100644
index 0000000000000..0fe917138693f
--- /dev/null
+++ b/testing/web-platform/tests/html/semantics/forms/form-submission-0/constructing-form-data-set.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<head>
+<meta charset="utf-8">
+<link rel="help" href="https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#constructing-the-form-data-set">
+<link ref="help" href="https://xhr.spec.whatwg.org/#dom-formdata">
+<link rel="help" href="https://fetch.spec.whatwg.org/#concept-bodyinit-extract">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+
+<iframe name="frame1"></iframe>
+<form accept-charset="iso-8859-1" target="frame1" action="/common/blank.html">
+<input type="hidden" name="_charset_">
+</form>
+
+<script>
+test(() => {
+  let formData = new FormData(document.querySelector('form'));
+  assert_equals(formData.get('_charset_'), 'UTF-8');
+}, 'FormData constructor always produces UTF-8 _charset_ value.');
+
+let t = async_test('_charset_ control sets the expected encoding name.');
+t.step(() => {
+  let iframe = document.querySelector('iframe');
+  iframe.onload = t.step_func_done(() => {
+    assert_not_equals(iframe.contentDocument.URL.indexOf('_charset_=windows-1252'), -1);
+  });
+  document.querySelector('form').submit();
+});
+</script>
+</body>
