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diff --git a/testing/web-platform/tests/html/syntax/speculative-charset/speculative-script.tentative.html b/testing/web-platform/tests/html/syntax/speculative-charset/speculative-script.tentative.html
new file mode 100644
index 0000000000..e665510946
--- /dev/null
+++ b/testing/web-platform/tests/html/syntax/speculative-charset/speculative-script.tentative.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="windows-1253">
+<title>Speculative script</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<script src=/common/utils.js></script>
+<body>
+<script>
+const uuid = token();
+
+window.onmessage = function(e) {
+  // The script is first speculatively loaded in the windows-1253 context (inherited from this doc), so
+  // the Greek hex NCR turns into a byte. This byte is stored. Then the script is fetched
+  // non-speculatively, because the Greek hexNCR in the URL makes the URL not match in the
+  // windows-1251 context. Now the Greek hex NCR turns in to a decimal NCR and the original Greek
+  // character comes back as a byte that gets a Cyrillic interpretation.
+  assert_equals(e.data, `token: ${uuid}, character: &#950;, previous character: \u0436, byte: \u0436`, "Check result");
+  done();
+}
+
+setup({single_test: true});
+const iframe = document.createElement('iframe');
+iframe.src = `support/speculative-script.py?uuid=${uuid}`;
+document.body.appendChild(iframe);
+</script>