diff --git a/testing/web-platform/tests/orientation-sensor/orientation-sensor-tests.js b/testing/web-platform/tests/orientation-sensor/orientation-sensor-tests.js
index a745bc885315..14023490a06f 100644
--- a/testing/web-platform/tests/orientation-sensor/orientation-sensor-tests.js
+++ b/testing/web-platform/tests/orientation-sensor/orientation-sensor-tests.js
@@ -42,7 +42,9 @@ async function checkPopulateMatrix(t, sensorProvider, sensorType) {
 
   
   assert_throws_js(TypeError,
-      () => sensor.populateMatrix(new Float32Array(new SharedArrayBuffer(16))));
+      
+      
+      () => sensor.populateMatrix(new Float32Array(new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer)));
 
   sensor.start();
 
diff --git a/testing/web-platform/tests/portals/portal-activate-data.html b/testing/web-platform/tests/portals/portal-activate-data.html
index 004fa97e55c0..260bb00ff068 100644
--- a/testing/web-platform/tests/portals/portal-activate-data.html
+++ b/testing/web-platform/tests/portals/portal-activate-data.html
@@ -74,7 +74,8 @@
   const w = await openBlankPortalHost();
   await promise_rejects_dom(
       t, 'DataCloneError', w.DOMException,
-      openPortalAndActivate('', {data: new SharedArrayBuffer}, w));
+      // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+      openPortalAndActivate('', {data: new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer}, w));
 }, "A SharedArrayBuffer cannot be passed through activate data.");
 
 promise_test(async t => {
diff --git a/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffer-interface/audiobuffer-copy-channel.html b/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffer-interface/audiobuffer-copy-channel.html
index 20780d94b730..c0cd49d32520 100644
--- a/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffer-interface/audiobuffer-copy-channel.html
+++ b/testing/web-platform/tests/webaudio/the-audio-api/the-audiobuffer-interface/audiobuffer-copy-channel.html
@@ -149,7 +149,9 @@
           buffer.copyFromChannel(x, 3);
         }, '7: buffer.copyFromChannel(x, 3)').throw(DOMException, 'IndexSizeError');
 
-        let shared_buffer = new Float32Array(new SharedArrayBuffer(32));
+        // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+        // WebAssembly.Memory's size is in multiples of 64 KiB
+        const shared_buffer = new Float32Array(new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer);
         should(
             () => {
               buffer.copyFromChannel(shared_buffer, 0);
@@ -202,7 +204,9 @@
           buffer.copyToChannel(x, 3);
         }, '6: buffer.copyToChannel(x, 3)').throw(DOMException, 'IndexSizeError');
 
-        let shared_buffer = new Float32Array(new SharedArrayBuffer(32));
+        // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+        // WebAssembly.Memory's size is in multiples of 64 KiB
+        const shared_buffer = new Float32Array(new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer);
         should(
             () => {
               buffer.copyToChannel(shared_buffer, 0);