diff --git a/dom/src/threads/nsDOMThreadService.cpp b/dom/src/threads/nsDOMThreadService.cpp
index 39ab40ce13cb..12d52164f8ff 100644
--- a/dom/src/threads/nsDOMThreadService.cpp
+++ b/dom/src/threads/nsDOMThreadService.cpp
@@ -558,7 +558,7 @@ DOMWorkerOperationCallback(JSContext* aCx)
     // above in which case we shouldn't wait here. We're guaranteed not to race
     // here because the pool reenters its monitor after canceling each worker
     // in order to notify its condition variable.
-    if (!worker->IsCanceled()) {
+    if (worker->IsSuspended() && !worker->IsCanceled()) {
       mon.Wait();
     }
   }
diff --git a/dom/src/threads/nsDOMWorkerPool.cpp b/dom/src/threads/nsDOMWorkerPool.cpp
index 17146b3ce6db..4c5b9001d8c3 100644
--- a/dom/src/threads/nsDOMWorkerPool.cpp
+++ b/dom/src/threads/nsDOMWorkerPool.cpp
@@ -164,9 +164,9 @@ nsDOMWorkerPool::NoteDyingWorker(nsDOMWorker* aWorker)
 void
 nsDOMWorkerPool::GetWorkers(nsTArray<nsDOMWorker*>& aArray)
 {
-  aArray.Clear();
+  PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
+  NS_ASSERTION(!aArray.Length(), "Should be empty!");
 
-  nsAutoMonitor mon(mMonitor);
 #ifdef DEBUG
   nsDOMWorker** newWorkers =
 #endif