core/modules/big_pipe/src/Render/BigPipeInterface.php | 4 ++++
 core/modules/big_pipe/src/Render/BigPipeResponse.php  | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/core/modules/big_pipe/src/Render/BigPipeInterface.php b/core/modules/big_pipe/src/Render/BigPipeInterface.php
index 988a512..c1baf60 100644
--- a/core/modules/big_pipe/src/Render/BigPipeInterface.php
+++ b/core/modules/big_pipe/src/Render/BigPipeInterface.php
@@ -128,6 +128,10 @@
  *
  * @see \Drupal\big_pipe\EventSubscriber\HtmlResponseBigPipeSubscriber
  * @see \Drupal\big_pipe\Render\Placeholder\BigPipeStrategy
+ *
+ * @internal
+ *   This object is marked as internal because it should only be used in the
+ *   BigPipe render pipeline.
  */
 interface BigPipeInterface {
 
diff --git a/core/modules/big_pipe/src/Render/BigPipeResponse.php b/core/modules/big_pipe/src/Render/BigPipeResponse.php
index 328a709..b578d8a 100644
--- a/core/modules/big_pipe/src/Render/BigPipeResponse.php
+++ b/core/modules/big_pipe/src/Render/BigPipeResponse.php
@@ -13,6 +13,10 @@
  *
  * @see \Drupal\big_pipe\Render\BigPipeInterface
  *
+ * @internal
+ *   This object is marked as internal because it should only be used in the
+ *   BigPipe render pipeline.
+ *
  * @todo Will become obsolete with https://www.drupal.org/node/2577631
  */
 class BigPipeResponse extends HtmlResponse {