diff --git a/testing/web-platform/tests/longtask-timing/longtask-before-observer.window.js b/testing/web-platform/tests/longtask-timing/longtask-before-observer.window.js
deleted file mode 100644
index b7d4eb9d1de1..000000000000
--- a/testing/web-platform/tests/longtask-timing/longtask-before-observer.window.js
+++ /dev/null
@@ -1,16 +0,0 @@
-async_test(t => {
-  assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
-  // Create a long task before any observer.
-  const begin = window.performance.now();
-  while (window.performance.now() < begin + 60);
-  // After a timeout, add an observer with buffered flag.
-  t.step_timeout(() => {
-    new PerformanceObserver(t.step_func_done(list => {
-      list.getEntries().forEach(entry => {
-        assert_equals(entry.entryType, 'longtask');
-        assert_equals(entry.name, 'self');
-        assert_greater_than(entry.duration, 50);
-      });
-    })).observe({type: 'longtask', buffered: true});
-  }, 0);
-}, 'PerformanceObserver with buffered flag can see previous longtask entries.');