diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index 6b2b93a1fb54..4bee876a1959 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -3526,9 +3526,15 @@ WorkerPrivate::GetClientState() const
 }
 
 const Maybe<ServiceWorkerDescriptor>
-WorkerPrivate::GetController() const
+WorkerPrivate::GetController()
 {
   AssertIsOnWorkerThread();
+  {
+    MutexAutoLock lock(mMutex);
+    if (mStatus >= Terminating) {
+      return Maybe<ServiceWorkerDescriptor>();
+    }
+  }
   MOZ_DIAGNOSTIC_ASSERT(mClientSource);
   return mClientSource->GetController();
 }
@@ -3537,9 +3543,15 @@ void
 WorkerPrivate::Control(const ServiceWorkerDescriptor& aServiceWorker)
 {
   AssertIsOnWorkerThread();
-  MOZ_DIAGNOSTIC_ASSERT(mClientSource);
   MOZ_DIAGNOSTIC_ASSERT(!IsChromeWorker());
   MOZ_DIAGNOSTIC_ASSERT(Type() != WorkerTypeService);
+  {
+    MutexAutoLock lock(mMutex);
+    if (mStatus >= Terminating) {
+      return;
+    }
+  }
+  MOZ_DIAGNOSTIC_ASSERT(mClientSource);
   mClientSource->SetController(aServiceWorker);
 }
 
diff --git a/dom/workers/WorkerPrivate.h b/dom/workers/WorkerPrivate.h
index d693fccbd5e2..90c10c1e423b 100644
--- a/dom/workers/WorkerPrivate.h
+++ b/dom/workers/WorkerPrivate.h
@@ -560,7 +560,7 @@ public:
   GetClientState() const;
 
   const Maybe<ServiceWorkerDescriptor>
-  GetController() const;
+  GetController();
 
   void
   Control(const ServiceWorkerDescriptor& aServiceWorker);