diff --git a/testing/web-platform/tests/compression/compression-bad-chunks.tentative.any.js b/testing/web-platform/tests/compression/compression-bad-chunks.tentative.any.js
index cc71b00030921..af210a765a7ea 100644
--- a/testing/web-platform/tests/compression/compression-bad-chunks.tentative.any.js
+++ b/testing/web-platform/tests/compression/compression-bad-chunks.tentative.any.js
@@ -28,13 +28,15 @@ const badChunks = [
     // Use a getter to postpone construction so that all tests don't fail where
     // SharedArrayBuffer is not yet implemented.
     get value() {
-      return new SharedArrayBuffer();
+      // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+      return new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer;
     }
   },
   {
     name: 'shared Uint8Array',
     get value() {
-      return new Uint8Array(new SharedArrayBuffer())
+      // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+      return new Uint8Array(new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer)
     }
   },
 ];
diff --git a/testing/web-platform/tests/compression/decompression-bad-chunks.tentative.any.js b/testing/web-platform/tests/compression/decompression-bad-chunks.tentative.any.js
index 51f369311588d..7dcb717a45cf0 100644
--- a/testing/web-platform/tests/compression/decompression-bad-chunks.tentative.any.js
+++ b/testing/web-platform/tests/compression/decompression-bad-chunks.tentative.any.js
@@ -28,13 +28,15 @@ const badChunks = [
     // Use a getter to postpone construction so that all tests don't fail where
     // SharedArrayBuffer is not yet implemented.
     get value() {
-      return new SharedArrayBuffer();
+      // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+      return new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer;
     }
   },
   {
     name: 'shared Uint8Array',
     get value() {
-      return new Uint8Array(new SharedArrayBuffer())
+      // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+      return new Uint8Array(new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer)
     }
   },
   {
diff --git a/testing/web-platform/tests/css/css-layout-api/constraints-data-sab-failure.https.html b/testing/web-platform/tests/css/css-layout-api/constraints-data-sab-failure.https.html
index 8659c2edef56a..b8df61c73d305 100644
--- a/testing/web-platform/tests/css/css-layout-api/constraints-data-sab-failure.https.html
+++ b/testing/web-platform/tests/css/css-layout-api/constraints-data-sab-failure.https.html
@@ -35,7 +35,8 @@
 
     try {
       childFragment = await child.layoutNextFragment({
-        data: { sab: new SharedArrayBuffer(4) }
+        // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+        data: { sab: new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer }
       });
     } catch(e) {
       // Success! The structured cloning algorithm should have thrown an error.
diff --git a/testing/web-platform/tests/css/css-layout-api/fragment-data-sab-failure.https.html b/testing/web-platform/tests/css/css-layout-api/fragment-data-sab-failure.https.html
index a6cfcf663dcf3..681de5b543c29 100644
--- a/testing/web-platform/tests/css/css-layout-api/fragment-data-sab-failure.https.html
+++ b/testing/web-platform/tests/css/css-layout-api/fragment-data-sab-failure.https.html
@@ -33,7 +33,8 @@
   async layout(children, edges, constraints, styleMap) {
     const childFragments = await Promise.all(children.map(child => child.layoutNextFragment()));
 
-    return {autoBlockSize: 0, childFragments, data: {sab: new SharedArrayBuffer(4) }};
+    // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+    return {autoBlockSize: 0, childFragments, data: {sab: new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer }};
   }
 });
 </script>
diff --git a/testing/web-platform/tests/xhr/send-data-sharedarraybuffer.any.js b/testing/web-platform/tests/xhr/send-data-sharedarraybuffer.any.js
index b902888f5600e..912f622697d53 100644
--- a/testing/web-platform/tests/xhr/send-data-sharedarraybuffer.any.js
+++ b/testing/web-platform/tests/xhr/send-data-sharedarraybuffer.any.js
@@ -1,8 +1,9 @@
 // META: title=XMLHttpRequest.send(sharedarraybuffer)
 
 test(() => {
-    var xhr = new XMLHttpRequest();
-    var buf = new SharedArrayBuffer();
+    const xhr = new XMLHttpRequest();
+    // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+    const buf = new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer;
 
     xhr.open("POST", "./resources/content.py", true);
     assert_throws_js(TypeError, function() {
@@ -13,8 +14,9 @@ test(() => {
 ["Int8Array", "Uint8Array", "Uint8ClampedArray", "Int16Array", "Uint16Array",
  "Int32Array", "Uint32Array", "Float32Array", "Float64Array", "DataView"].forEach((type) => {
     test(() => {
-        var xhr = new XMLHttpRequest();
-        var arr = new self[type](new SharedArrayBuffer());
+        const xhr = new XMLHttpRequest();
+        // See https://github.com/whatwg/html/issues/5380 for why not `new SharedArrayBuffer()`
+        const arr = new self[type](new WebAssembly.Memory({ shared:true, initial:1, maximum:1 }).buffer);
 
         xhr.open("POST", "./resources/content.py", true);
         assert_throws_js(TypeError, function() {