diff --git a/core/modules/workflows/src/StateInterface.php b/core/modules/workflows/src/StateInterface.php
index 771658cd25..6cc8ace95c 100644
--- a/core/modules/workflows/src/StateInterface.php
+++ b/core/modules/workflows/src/StateInterface.php
@@ -4,6 +4,10 @@
 
 /**
  * An interface for state value objects.
+ *
+ * @internal
+ *   The StateInterface should only be used by Workflows and Content Moderation.
+ *   @todo Revisit the need for this in https://www.drupal.org/node/2902309.
  */
 interface StateInterface {
 
diff --git a/core/modules/workflows/src/TransitionInterface.php b/core/modules/workflows/src/TransitionInterface.php
index 7db34e8dd9..0fa159cabf 100644
--- a/core/modules/workflows/src/TransitionInterface.php
+++ b/core/modules/workflows/src/TransitionInterface.php
@@ -4,6 +4,11 @@
 
 /**
  * A transition value object that describes the transition between two states.
+ *
+ * @internal
+ *   The TransitionInterface should only be used by Workflows and Content
+ *   Moderation.
+ *   @todo Revisit the need for this in https://www.drupal.org/node/2902309.
  */
 interface TransitionInterface {