diff --git a/dom/workers/ServiceWorkerManager.cpp b/dom/workers/ServiceWorkerManager.cpp
index 347db83201f4..2503caac6d74 100644
--- a/dom/workers/ServiceWorkerManager.cpp
+++ b/dom/workers/ServiceWorkerManager.cpp
@@ -2361,7 +2361,10 @@ ServiceWorkerManager::IsControlled(nsIDocument* aDoc, bool* aIsControlled)
   MOZ_ASSERT(aIsControlled);
   nsRefPtr<ServiceWorkerRegistrationInfo> registration;
   nsresult rv = GetDocumentRegistration(aDoc, getter_AddRefs(registration));
-  NS_ENSURE_SUCCESS(rv, rv);
+  if (NS_WARN_IF(NS_FAILED(rv) && rv != NS_ERROR_NOT_AVAILABLE)) {
+    // It's OK to ignore the case where we don't have a registration.
+    return rv;
+  }
   *aIsControlled = !!registration;
   return NS_OK;
 }
@@ -2372,7 +2375,7 @@ ServiceWorkerManager::GetDocumentRegistration(nsIDocument* aDoc,
 {
   nsRefPtr<ServiceWorkerRegistrationInfo> registration;
   if (!mControlledDocuments.Get(aDoc, getter_AddRefs(registration))) {
-    return NS_ERROR_FAILURE;
+    return NS_ERROR_NOT_AVAILABLE;
   }
 
   // If the document is controlled, the current worker MUST be non-null.