diff --git a/packages/service-worker/worker/src/driver.ts b/packages/service-worker/worker/src/driver.ts
index 7837b45d89..a80b69ede5 100644
--- a/packages/service-worker/worker/src/driver.ts
+++ b/packages/service-worker/worker/src/driver.ts
@@ -224,7 +224,7 @@ export class Driver implements Debuggable, UpdateSource {
     }
 
     // Handle the push and keep the SW alive until it's handled.
-    msg.waitUntil(this.handlePush(msg.data));
+    msg.waitUntil(this.handlePush(msg.data.json()));
   }
 
   private async handleMessage(msg: MsgAny&{action: string}, from: Client): Promise<void> {
diff --git a/packages/service-worker/worker/testing/scope.ts b/packages/service-worker/worker/testing/scope.ts
index bb97a2deaa..2599c04a36 100644
--- a/packages/service-worker/worker/testing/scope.ts
+++ b/packages/service-worker/worker/testing/scope.ts
@@ -324,7 +324,10 @@ class MockMessageEvent extends MockExtendableEvent {
 }
 
 class MockPushEvent extends MockExtendableEvent {
-  constructor(readonly data: Object) { super(); }
+  constructor(private _data: Object) { super(); }
+  data = {
+    json: () => this._data,
+  };
 }
 
 class MockInstallEvent extends MockExtendableEvent {}