--- a/dom/workers/ServiceWorkerUpdaterChild.cpp
+++ b/dom/workers/ServiceWorkerUpdaterChild.cpp
@@ -11,21 +11,24 @@ namespace dom {
 namespace workers {
 
 ServiceWorkerUpdaterChild::ServiceWorkerUpdaterChild(GenericPromise* aPromise,
                                                      CancelableRunnable* aSuccessRunnable,
                                                      CancelableRunnable* aFailureRunnable)
   : mSuccessRunnable(aSuccessRunnable)
   , mFailureRunnable(aFailureRunnable)
 {
+  // TODO: remove the main thread restriction after fixing bug 1364821.
+  MOZ_ASSERT(NS_IsMainThread());
+
   MOZ_ASSERT(aPromise);
   MOZ_ASSERT(aSuccessRunnable);
   MOZ_ASSERT(aFailureRunnable);
 
-  aPromise->Then(AbstractThread::GetCurrent(), __func__,
+  aPromise->Then(AbstractThread::MainThread(), __func__,
     [this]() {
       mPromiseHolder.Complete();
       Unused << Send__delete__(this);
   }).Track(mPromiseHolder);
 }
 
 mozilla::ipc::IPCResult
 ServiceWorkerUpdaterChild::RecvProceed(const bool& aAllowed)