diff --git a/server/src/main/java/org/elasticsearch/cluster/routing/allocation/DataTier.java b/server/src/main/java/org/elasticsearch/cluster/routing/allocation/DataTier.java
index 5a5c7c740e674..34bda24bde330 100644
--- a/server/src/main/java/org/elasticsearch/cluster/routing/allocation/DataTier.java
+++ b/server/src/main/java/org/elasticsearch/cluster/routing/allocation/DataTier.java
@@ -175,6 +175,7 @@ public Settings getAdditionalIndexSettings(String indexName, boolean isDataStrea
         }
     }
 
+    // visible for testing
     static final class DataTierSettingValidator implements Setting.Validator<String> {
 
         private static final Collection<Setting<?>> dependencies = List.of(