diff --git a/dom/workers/RuntimeService.cpp b/dom/workers/RuntimeService.cpp
index d97e538fce3..66573fd2eee 100644
--- a/dom/workers/RuntimeService.cpp
+++ b/dom/workers/RuntimeService.cpp
@@ -1668,7 +1668,7 @@ RuntimeService::UnregisterWorker(JSContext* aCx, WorkerPrivate* aWorkerPrivate)
       }
     }
 
-    if (!domainInfo->ActiveWorkerCount()) {
+    if (domainInfo->HasNoWorkers()) {
       MOZ_ASSERT(domainInfo->mQueuedWorkers.IsEmpty());
       mDomainMap.Remove(domain);
     }
diff --git a/dom/workers/RuntimeService.h b/dom/workers/RuntimeService.h
index aa27cc085bc..984c32b6f8c 100644
--- a/dom/workers/RuntimeService.h
+++ b/dom/workers/RuntimeService.h
@@ -56,9 +56,21 @@ class RuntimeService final : public nsIObserver
     ActiveWorkerCount() const
     {
       return mActiveWorkers.Length() +
-             mActiveServiceWorkers.Length() +
              mChildWorkerCount;
     }
+
+    uint32_t
+    ActiveServiceWorkerCount() const
+    {
+      return mActiveServiceWorkers.Length();
+    }
+
+    bool
+    HasNoWorkers() const
+    {
+      return ActiveWorkerCount() == 0 &&
+             ActiveServiceWorkerCount() == 0;
+    }
   };
 
   struct IdleThreadInfo;