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diff --git a/testing/web-platform/tests/html/semantics/scripting-1/the-script-element/async_003.htm b/testing/web-platform/tests/html/semantics/scripting-1/the-script-element/async_003.htm
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+++ b/testing/web-platform/tests/html/semantics/scripting-1/the-script-element/async_003.htm
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>An async script does not block the parser while downloading</title>
+        <meta name="timeout" content="long">
+        <meta http-equiv="content-type" content="text/html; charset=UTF-8" />
+        <meta description="This test ensures an async script does not block the parser while downloading." />
+        <link rel="author" title="Microsoft" href="http://www.microsoft.com/" />
+        <link rel="help" href="https://html.spec.whatwg.org/multipage/#attr-script-async"/>
+        <script src="/resources/testharness.js"></script>
+        <script src="/resources/testharnessreport.js"></script>
+    </head>
+    <body>
+        <div id=log></div>
+        <script type="text/javascript">
+        var t = async_test("An async script does not block the parser while downloading");
+
+        function timeout()
+        {
+            t.step(function(){ assert_equals(document.getElementById("testresult").innerHTML, "21")});
+            t.done();
+        }
+
+        var timer = setTimeout(timeout, 4000);
+
+        function log(text)
+        {
+            var textNode = document.createTextNode(text);
+            document.getElementById("testresult").appendChild(textNode);
+        }
+        </script>
+
+        <span id="testresult"></span>
+
+        <script src="log.py?sec=3&id=1" async></script>
+        <script>
+            log('2');
+        </script>
+    </body>
+</html>