diff --git a/dom/fetch/Fetch.cpp b/dom/fetch/Fetch.cpp
index 7468b5545cb..8cd2ec76335 100644
--- a/dom/fetch/Fetch.cpp
+++ b/dom/fetch/Fetch.cpp
@@ -136,11 +136,6 @@ public:
     nsCOMPtr<nsILoadGroup> loadGroup = proxy->GetWorkerPrivate()->GetLoadGroup();
     MOZ_ASSERT(loadGroup);
     RefPtr<FetchDriver> fetch = new FetchDriver(mRequest, principal, loadGroup);
-    nsIDocument* doc = proxy->GetWorkerPrivate()->GetDocument();
-    if (doc) {
-      fetch->SetDocument(doc);
-    }
-
     nsresult rv = fetch->Fetch(mResolver);
     // Right now we only support async fetch, which should never directly fail.
     if (NS_WARN_IF(NS_FAILED(rv))) {
diff --git a/dom/fetch/FetchDriver.cpp b/dom/fetch/FetchDriver.cpp
index cdc62db8eca..50c31bec433 100644
--- a/dom/fetch/FetchDriver.cpp
+++ b/dom/fetch/FetchDriver.cpp
@@ -241,10 +241,8 @@ FetchDriver::HttpFetch()
   MOZ_ASSERT(mLoadGroup);
   nsCOMPtr<nsIChannel> chan;
 
-  // For dedicated workers mDocument refers to the parent document of the
-  // worker (why do we do that?). In that case we don't want to use the
-  // document here since that is not the correct principal.
-  if (mDocument && mDocument->NodePrincipal() == mPrincipal) {
+  if (mDocument) {
+    MOZ_ASSERT(mDocument->NodePrincipal() == mPrincipal);
     rv = NS_NewChannel(getter_AddRefs(chan),
                        uri,
                        mDocument,