diff --git a/testing/web-platform/tests/media-source/dedicated-worker/mediasource-worker-handle.html b/testing/web-platform/tests/media-source/dedicated-worker/mediasource-worker-handle.html
index a921acdec9e40..6129e05ffb4a8 100644
--- a/testing/web-platform/tests/media-source/dedicated-worker/mediasource-worker-handle.html
+++ b/testing/web-platform/tests/media-source/dedicated-worker/mediasource-worker-handle.html
@@ -34,15 +34,17 @@
 }, "Test main context receipt of postMessage'd MediaSourceHandle from DedicatedWorker MediaSource");
 
 test(t => {
-  assert_true(window.hasOwnProperty("MediaSourceHandle"), "window must have MediaSourceHandle visibility");
+  assert_true(window.hasOwnProperty("MediaSourceHandle"), "window must have MediaSourceHandle");
+}, "Test main-thread has MediaSourceHandle defined");
 
+test(t => {
   // Note, MSE spec may eventually describe how a main-thread MediaSource can
   // attach to an HTMLMediaElement using a MediaSourceHandle. For now, we
-  // ensure that the implementation of this is not available.
-  assert_throws_dom('NotSupportedError', function() {
-    let h = new MediaSource().handle;
-  }, 'main thread MediaSource instance cannot (yet) create a usable MediaSourceHandle');
-}, "Test main-thread-owned MediaSource instance cannot create a MediaSourceHandle");
+  // ensure that the implementation of this is not available per current spec.
+  assert_false(
+      "handle" in MediaSource.prototype,
+      "window MediaSource must not have handle in prototype");
+}, "Test main-thread MediaSource does not have handle getter");
 
 if (MediaSource.hasOwnProperty("canConstructInDedicatedWorker") && MediaSource.canConstructInDedicatedWorker === true) {
   // If implementation claims support for MSE-in-Workers, then fetch and run