diff --git a/lucene/misc/src/java/org/apache/lucene/index/sorter/BlockJoinComparatorSource.java b/lucene/misc/src/java/org/apache/lucene/index/sorter/BlockJoinComparatorSource.java
index 6d5ff0b..af91463 100644
--- a/lucene/misc/src/java/org/apache/lucene/index/sorter/BlockJoinComparatorSource.java
+++ b/lucene/misc/src/java/org/apache/lucene/index/sorter/BlockJoinComparatorSource.java
@@ -41,6 +41,7 @@
  *    <li>Cannot yet be used with {@link IndexSearcher#searchAfter(ScoreDoc, Query, int, Sort) IndexSearcher.searchAfter}
  *    <li>Filling sort field values is not yet supported.
  * </ul>
+ * @lucene.experimental
  */
 // TODO: can/should we clean this thing up (e.g. return a proper sort value)
 // and move to the join/ module?