diff --git a/CHANGELOG.md b/CHANGELOG.md
index e836629..27a1582 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,9 @@ This library adheres to [Semantic Versioning](https://semver.org/) and [Keep a C
 
 ## Unreleased
 
-Nothing yet.
+### Deprecated
+
+- `Used_Post_IDs` class.
 
 ## 2.2.0
 
diff --git a/src/alley/wp/post-ids/class-used-post-ids.php b/src/alley/wp/post-ids/class-used-post-ids.php
index 9f92187..3555ce8 100644
--- a/src/alley/wp/post-ids/class-used-post-ids.php
+++ b/src/alley/wp/post-ids/class-used-post-ids.php
@@ -11,6 +11,8 @@
 
 /**
  * Track post IDs that have been used, e.g. while rendering a page.
+ *
+ * @deprecated No longer recommended.
  */
 final class Used_Post_IDs implements Post_IDs {
 	/**