diff --git a/api/peer_connection_interface.h b/api/peer_connection_interface.h
index 8a6ae960bd..7e16ad96be 100644
--- a/api/peer_connection_interface.h
+++ b/api/peer_connection_interface.h
@@ -1421,6 +1421,8 @@ struct RTC_EXPORT PeerConnectionFactoryDependencies final {
   rtc::Thread* worker_thread = nullptr;
   rtc::Thread* signaling_thread = nullptr;
   rtc::SocketFactory* socket_factory = nullptr;
+  // The `packet_socket_factory` will only be used if CreatePeerConnection is
+  // called without a `port_allocator`.
   std::unique_ptr<rtc::PacketSocketFactory> packet_socket_factory;
   std::unique_ptr<TaskQueueFactory> task_queue_factory;
   std::unique_ptr<cricket::MediaEngineInterface> media_engine;