diff --git a/dom/workers/ServiceWorkerRegistrationInfo.cpp b/dom/workers/ServiceWorkerRegistrationInfo.cpp
index 5fa01bef3c2e..d6a93c1f994c 100644
--- a/dom/workers/ServiceWorkerRegistrationInfo.cpp
+++ b/dom/workers/ServiceWorkerRegistrationInfo.cpp
@@ -240,10 +240,8 @@ ServiceWorkerRegistrationInfo::Activate()
 
   // FIXME(nsm): Unlink appcache if there is one.
 
-  RefPtr<ServiceWorkerManager> swm = ServiceWorkerManager::GetInstance();
-  swm->CheckPendingReadyPromises();
-
   // "Queue a task to fire a simple event named controllerchange..."
+  RefPtr<ServiceWorkerManager> swm = ServiceWorkerManager::GetInstance();
   nsCOMPtr<nsIRunnable> controllerChangeRunnable =
     NewRunnableMethod<RefPtr<ServiceWorkerRegistrationInfo>>(
       swm, &ServiceWorkerManager::FireControllerChange, this);
@@ -319,6 +317,10 @@ ServiceWorkerRegistrationInfo::AsyncUpdateRegistrationStateProperties(WhichServi
   } else {
     MOZ_ASSERT(aTransition == TransitionToNextState);
     swm->TransitionServiceWorkerRegistrationWorker(this, aWorker);
+
+    if (aWorker == WhichServiceWorker::WAITING_WORKER) {
+      swm->CheckPendingReadyPromises();
+    }
   }
 }
 
diff --git a/dom/workers/test/serviceworkers/test_worker_reference_gc_timeout.html b/dom/workers/test/serviceworkers/test_worker_reference_gc_timeout.html
index a94eb2310cf8..8666495ac8c9 100644
--- a/dom/workers/test/serviceworkers/test_worker_reference_gc_timeout.html
+++ b/dom/workers/test/serviceworkers/test_worker_reference_gc_timeout.html
@@ -28,7 +28,6 @@ add_task(function setupPrefs() {
   ]});
 });
 
-//var worker;
 add_task(function* test_worker_ref_gc() {
   let registration = yield navigator.serviceWorker.register(
     "lazy_worker.js", { scope: "./lazy_worker_scope_timeout"} )
@@ -45,10 +44,32 @@ add_task(function* test_worker_ref_gc() {
         });
       });
     });
-
   ok(true, "Got activated event!");
 
   yield registration.unregister();
+});
+
+add_task(function* test_worker_ref_gc_ready_promise() {
+  let wait_active = navigator.serviceWorker.ready.then(function(reg) {
+    SpecialPowers.exactGC();
+    ok(reg.active, "Got active worker.");
+    ok(reg.active.state === "activating", "Worker is in activating state");
+    return new Promise(function(res) {
+      reg.active.onstatechange = function(e) {
+        reg.active.onstatechange = null;
+        ok(reg.active.state === "activated", "Worker was activated");
+        res();
+      }
+    });
+  });
+
+  let registration = yield navigator.serviceWorker.register(
+    "lazy_worker.js", { scope: "."} );
+  yield wait_active;
+  yield registration.unregister();
+});
+
+add_task(function* cleanup() {
   yield SpecialPowers.popPrefEnv();
 });
 </script>