--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -600,19 +600,17 @@ private:
   }
 };
 
 class CloseEventRunnable final : public WorkerRunnable
 {
 public:
   explicit CloseEventRunnable(WorkerPrivate* aWorkerPrivate)
   : WorkerRunnable(aWorkerPrivate, WorkerThreadUnchangedBusyCount)
-  {
-    aWorkerPrivate->CloseHandlerStarted();
-  }
+  { }
 
 private:
   virtual bool
   PreDispatch(WorkerPrivate* aWorkerPrivate) override
   {
     MOZ_CRASH("Don't call Dispatch() on CloseEventRunnable!");
   }
 
@@ -620,16 +618,18 @@ private:
   PostDispatch(WorkerPrivate* aWorkerPrivate, bool aDispatchResult) override
   {
     MOZ_CRASH("Don't call Dispatch() on CloseEventRunnable!");
   }
 
   virtual bool
   WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
   {
+    aWorkerPrivate->CloseHandlerStarted();
+
     WorkerGlobalScope* globalScope = aWorkerPrivate->GlobalScope();
 
     RefPtr<Event> event = NS_NewDOMEvent(globalScope, nullptr, nullptr);
 
     event->InitEvent(NS_LITERAL_STRING("close"), false, false);
     event->SetTrusted(true);
 
     globalScope->DispatchDOMEvent(nullptr, event, nullptr, nullptr);