diff --git a/x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/TSDataGenerationHelper.java b/x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/TSDataGenerationHelper.java
index 6fb374c2be5b2..7eb7b041bd1f1 100644
--- a/x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/TSDataGenerationHelper.java
+++ b/x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/TSDataGenerationHelper.java
@@ -54,9 +54,7 @@ private static Object randomDimensionValue(String dimensionName) {
         // Making a list-to-set-to-list to ensure uniqueness.
         this.numDocs = numDocs;
         var maxAttributes = (int) Math.sqrt(numDocs);
-        List<String> tempAttributeSet = List.copyOf(
-            Set.copyOf(ESTestCase.randomList(1, maxAttributes, () -> ESTestCase.randomAlphaOfLengthBetween(3, 30)))
-        );
+        List<String> tempAttributeSet = ESTestCase.randomList(1, maxAttributes, () -> ESTestCase.randomAlphaOfLengthBetween(3, 30));
         var maxTimeSeries = (int) Math.sqrt(numDocs);
         var minTimeSeries = Math.max(1, maxTimeSeries / 4);
         numTimeSeries = ESTestCase.randomIntBetween(minTimeSeries, maxTimeSeries);