diff --git a/css-typed-om/styleMap-update-function.html b/css-typed-om/styleMap-update-function.html
new file mode 100644
index 00000000000000..4ca5e0ee914919
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+++ b/css-typed-om/styleMap-update-function.html
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+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>styleMap objects provide an 'update' function</title>
+<meta name="author" title="Shane Stephens">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <div id='element'></div>
+  <div id="log"></div>
+  <script>
+    test(function() {
+      element.styleMap.set('width', new CSSSimpleLength(42, 'px'));
+      element.styleMap.update('width', length => new CSSSimpleLength(length.value + 20, length.type))
+      assert_equals(element.styleMap.get('width').value, 62, 'update expected to apply callback to old value in map');
+    });
+  </script>
+
