diff --git a/server/src/main/java/org/elasticsearch/rest/action/document/RestBulkAction.java b/server/src/main/java/org/elasticsearch/rest/action/document/RestBulkAction.java
index 2d77093426727..925f5c68f9835 100644
--- a/server/src/main/java/org/elasticsearch/rest/action/document/RestBulkAction.java
+++ b/server/src/main/java/org/elasticsearch/rest/action/document/RestBulkAction.java
@@ -105,7 +105,7 @@ private class ChunkHandler implements BaseRestHandler.RequestBodyChunkConsumer {
 
         private volatile RestChannel restChannel;
         private final ArrayDeque<ReleasableBytesReference> unParsedChunks = new ArrayDeque<>(4);
-        private ArrayList<DocWriteRequest<?>> items = new ArrayList<>(4);
+        private final ArrayList<DocWriteRequest<?>> items = new ArrayList<>(4);
 
         private ChunkHandler(RestRequest request) {
             this.request = request;