diff --git a/netwerk/ipc/NeckoChild.cpp b/netwerk/ipc/NeckoChild.cpp
index 9b0ad46f9f57..fbef3725ccd1 100644
--- a/netwerk/ipc/NeckoChild.cpp
+++ b/netwerk/ipc/NeckoChild.cpp
@@ -119,9 +119,9 @@ NeckoChild::AllocPAltDataOutputStreamChild(
         const nsCString& type,
         PHttpChannelChild* channel)
 {
-  AltDataOutputStreamChild* stream = new AltDataOutputStreamChild();
-  stream->AddIPDLReference();
-  return stream;
+  // We don't allocate here: see HttpChannelChild::OpenAlternativeOutputStream()
+  NS_NOTREACHED("AllocPAltDataOutputStreamChild should not be called");
+  return nullptr;
 }
 
 bool
diff --git a/netwerk/protocol/http/HttpChannelChild.cpp b/netwerk/protocol/http/HttpChannelChild.cpp
index f50415de2091..41d125aae715 100644
--- a/netwerk/protocol/http/HttpChannelChild.cpp
+++ b/netwerk/protocol/http/HttpChannelChild.cpp
@@ -2715,8 +2715,20 @@ HttpChannelChild::OpenAlternativeOutputStream(const nsACString & aType, nsIOutpu
     return NS_ERROR_NOT_AVAILABLE;
   }
 
-  RefPtr<AltDataOutputStreamChild> stream =
-    static_cast<AltDataOutputStreamChild*>(gNeckoChild->SendPAltDataOutputStreamConstructor(nsCString(aType), this));
+  nsCOMPtr<nsIEventTarget> neckoTarget = GetNeckoTarget();
+  MOZ_ASSERT(neckoTarget);
+
+  RefPtr<AltDataOutputStreamChild> stream = new AltDataOutputStreamChild();
+  stream->AddIPDLReference();
+
+  gNeckoChild->SetEventTargetForActor(stream, neckoTarget);
+
+  if (!gNeckoChild->SendPAltDataOutputStreamConstructor(stream,
+                                                        nsCString(aType),
+                                                        this)) {
+    return NS_ERROR_FAILURE;
+  }
+
   stream.forget(_retval);
   return NS_OK;
 }