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diff --git a/testing/web-platform/tests/element-timing/progressively-loaded-image.html b/testing/web-platform/tests/element-timing/progressively-loaded-image.html
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+++ b/testing/web-platform/tests/element-timing/progressively-loaded-image.html
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+<meta charset=utf-8 />
+<title>Element Timing: buffer elements before onload</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<script src="resources/element-timing-helpers.js"></script>
+<body>
+<script>
+  let beforeRender;
+  let img;
+  // Number of characters to be read on the initial read, before sleeping.
+  // Should be sufficient to do at least a first scan.
+  let numInitial = 75;
+  let sleep = 500;
+  async_test(function(t) {
+    assert_implements(window.PerformanceElementTiming, "PerformanceElementTiming is not implemented");
+    const img_src = 'resources/progressive-image.py?name=square20.jpg&numInitial='
+      + numInitial + '&sleep=' + sleep;
+    const observer = new PerformanceObserver(
+      t.step_func_done(function(entryList) {
+        assert_equals(entryList.getEntries().length, 1);
+        const entry = entryList.getEntries()[0];
+        const pathname = window.location.origin + '/element-timing/' + img_src;
+        // Since the image is only fully loaded after the sleep, the render timestamp
+        // must be greater than |beforeRender| + |sleep|.
+        checkElement(entry, pathname, 'my_image', '', beforeRender + sleep, img);
+        checkNaturalSize(entry, 20, 20);
+      })
+    );
+    observer.observe({entryTypes: ['element']});
+
+    img = document.createElement('img');
+    img.src = img_src;
+    img.setAttribute('elementtiming', 'my_image');
+    document.body.appendChild(img);
+    beforeRender = performance.now();
+    t.step_timeout(() => {assert_true(0);}, 2000);
+  }, "Element Timing: image render timestamp occurs after it is fully loaded.");
+</script>