diff --git a/dom/fetch/Fetch.cpp b/dom/fetch/Fetch.cpp
index 53ada9378b..dfc65c840e 100644
--- a/dom/fetch/Fetch.cpp
+++ b/dom/fetch/Fetch.cpp
@@ -1139,6 +1139,10 @@ FetchBody<Derived>::LockStream(JSContext* aCx,
                                JS::HandleObject aStream,
                                ErrorResult& aRv)
 {
+  MOZ_ASSERT(JS::ReadableStreamGetMode(aStream) ==
+               JS::ReadableStreamMode::ExternalSource);
+
+  // This is native stream, creating a reader will not execute any JS code.
   JS::Rooted<JSObject*> reader(aCx,
                                JS::ReadableStreamGetReader(aCx, aStream,
                                                            JS::ReadableStreamReaderMode::Default));
diff --git a/dom/fetch/FetchStreamReader.cpp b/dom/fetch/FetchStreamReader.cpp
index 98d2588a0e..5d9719a0c1 100644
--- a/dom/fetch/FetchStreamReader.cpp
+++ b/dom/fetch/FetchStreamReader.cpp
@@ -169,17 +169,13 @@ FetchStreamReader::OnOutputStreamReady(nsIAsyncOutputStream* aStream)
     return WriteBuffer();
   }
 
-  AutoJSAPI jsapi;
-  if (NS_WARN_IF(!jsapi.Init(mGlobal))) {
-    CloseAndRelease(NS_ERROR_DOM_INVALID_STATE_ERR);
-    return NS_ERROR_FAILURE;
-  }
+  // TODO: We need to verify this is the correct global per the spec.
+  //       See bug 1385890.
+  AutoEntryScript aes(mGlobal, "ReadableStreamReader.read", !mWorkerHolder);
 
-  JSContext* cx = jsapi.cx();
-
-  JS::Rooted<JSObject*> reader(cx, mReader);
-  JS::Rooted<JSObject*> promise(cx,
-                                JS::ReadableStreamDefaultReaderRead(cx,
+  JS::Rooted<JSObject*> reader(aes.cx(), mReader);
+  JS::Rooted<JSObject*> promise(aes.cx(),
+                                JS::ReadableStreamDefaultReaderRead(aes.cx(),
                                                                     reader));
   if (NS_WARN_IF(!promise)) {
     // Let's close the stream.