diff --git a/common/performance-timeline-utils.js b/common/performance-timeline-utils.js
index 6845d6cbc689fc..d50da5a833040f 100644
--- a/common/performance-timeline-utils.js
+++ b/common/performance-timeline-utils.js
@@ -42,3 +42,10 @@ function test_entries(actualEntries, expectedEntries) {
     }
   })
 }
+
+function delayedLoadListener(callback) {
+  window.addEventListener('load', function() {
+    // TODO(cvazac) Remove this setTimeout when spec enforces sync entries
+    setTimeout(callback, 0)
+  })
+}
diff --git a/server-timing/cross_origin.https.html b/server-timing/cross_origin.https.html
index 1421b38a05eb8c..d31c7b006caf23 100644
--- a/server-timing/cross_origin.https.html
+++ b/server-timing/cross_origin.https.html
@@ -2,7 +2,7 @@
 <head>
     <meta charset='utf-8' />
     <script src="/resources/testharness.js"></script>
-    <script src='/resources/testharnessreport.js'></script>
+    <script src="/resources/testharnessreport.js"></script>
     <script src="/common/performance-timeline-utils.js"></script>
     <script src="/common/get-host-info.sub.js"></script>
     <script>
@@ -20,7 +20,7 @@
         document.getElementsByTagName('script')[0].parentNode.appendChild(img)
       })
 
-      window.addEventListener('load', function() {
+      delayedLoadListener(function() {
         function assertServerTimingEntries(url, expectedEntryCount) {
           test_equals(performance.getEntriesByName(url)[0].serverTiming.length,
             expectedEntryCount,
diff --git a/server-timing/navigation_timing_idl.https.html b/server-timing/navigation_timing_idl.https.html
index 290bb889b14933..d911d64e47ced0 100644
--- a/server-timing/navigation_timing_idl.https.html
+++ b/server-timing/navigation_timing_idl.https.html
@@ -2,10 +2,11 @@
 <head>
     <meta charset='utf-8' />
     <script src="/resources/testharness.js"></script>
-    <script src='/resources/testharnessreport.js'></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="/common/performance-timeline-utils.js"></script>
     <script>
       setup({explicit_done: true})
-      window.addEventListener('load', function(){
+      delayedLoadListener(function(){
         assert_not_equals(typeof performance.getEntriesByType('navigation')[0].serverTiming, 'undefined',
           'An instance of `PerformanceNavigationTiming` should have a `serverTiming` attribute.')
         done()
diff --git a/server-timing/resource_timing_idl.https.html b/server-timing/resource_timing_idl.https.html
index d2c3c9274eab86..b1d8699cc60574 100644
--- a/server-timing/resource_timing_idl.https.html
+++ b/server-timing/resource_timing_idl.https.html
@@ -2,10 +2,11 @@
 <head>
     <meta charset='utf-8' />
     <script src="/resources/testharness.js"></script>
-    <script src='/resources/testharnessreport.js'></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="/common/performance-timeline-utils.js"></script>
     <script>
       setup({explicit_done: true})
-      window.addEventListener('load', function(){
+      delayedLoadListener(function(){
         assert_not_equals(typeof performance.getEntriesByType('resource')[0].serverTiming, 'undefined',
           'An instance of `PerformanceResourceTiming` should have a `serverTiming` attribute.')
         done()
diff --git a/server-timing/server_timing_header-parsing.https.html b/server-timing/server_timing_header-parsing.https.html
index 156dfcd344f36c..7469c55c9a5bc4 100644
--- a/server-timing/server_timing_header-parsing.https.html
+++ b/server-timing/server_timing_header-parsing.https.html
@@ -7,7 +7,8 @@
 <head>
     <meta charset='utf-8' />
     <script src="/resources/testharness.js"></script>
-    <script src='/resources/testharnessreport.js'></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="/common/performance-timeline-utils.js"></script>
     <script src="/common/performance-timeline-utils.js"></script>
     <script>
       setup({explicit_done: true})
@@ -49,6 +50,6 @@
         document.getElementsByTagName('head')[0].appendChild(script)
         urlToIndex[script.src] = i
       }
-      window.addEventListener('load', runTests)
+      delayedLoadListener(runTests)
     </script>
 </head>
diff --git a/server-timing/service_worker_idl.https.html b/server-timing/service_worker_idl.https.html
index 1c1be8995b3310..5c493fdcb0ab58 100644
--- a/server-timing/service_worker_idl.https.html
+++ b/server-timing/service_worker_idl.https.html
@@ -2,7 +2,7 @@
 <head>
     <meta charset='utf-8' />
     <script src="/resources/testharness.js"></script>
-    <script src='/resources/testharnessreport.js'></script>
+    <script src="/resources/testharnessreport.js"></script>
     <script>
       (async () => {
         const scope = 'does/not/exist'
diff --git a/server-timing/test_server_timing.https.html b/server-timing/test_server_timing.https.html
index 2d43aa2d43b722..4f3554aa4a4572 100644
--- a/server-timing/test_server_timing.https.html
+++ b/server-timing/test_server_timing.https.html
@@ -2,12 +2,12 @@
 <head>
     <meta charset='utf-8' />
     <script src="/resources/testharness.js"></script>
-    <script src='/resources/testharnessreport.js'></script>
+    <script src="/resources/testharnessreport.js"></script>
     <script src="/common/performance-timeline-utils.js"></script>
     <script>
       setup({explicit_done: true})
 
-      window.addEventListener('load', function() {
+      delayedLoadListener(function() {
         // there should be exactly three server-timing entries, 2 for document, 1 for img#one
         test_entries(performance.getEntriesByType('navigation')[0].serverTiming, [{
           duration: 1.1,
