diff --git a/server/src/main/java/org/elasticsearch/ingest/IngestCtxMap.java b/server/src/main/java/org/elasticsearch/ingest/IngestCtxMap.java
index b648051669567..e3cdc13e1c11e 100644
--- a/server/src/main/java/org/elasticsearch/ingest/IngestCtxMap.java
+++ b/server/src/main/java/org/elasticsearch/ingest/IngestCtxMap.java
@@ -13,7 +13,6 @@
 import org.elasticsearch.script.Metadata;
 
 import java.time.ZonedDateTime;
-import java.util.HashMap;
 import java.util.Map;
 
 /**
@@ -32,7 +31,9 @@
 class IngestCtxMap extends CtxMap {
 
     /**
-     * Create an IngestCtxMap with the given metadata, source and default validators
+     * Create an IngestCtxMap with the given metadata, source and default validators.
+     *
+     * Source is not copied, callers can observe changes to source.
      */
     IngestCtxMap(
         String index,
@@ -43,7 +44,7 @@ class IngestCtxMap extends CtxMap {
         ZonedDateTime timestamp,
         Map<String, Object> source
     ) {
-        super(new HashMap<>(source), new IngestDocMetadata(index, id, version, routing, versionType, timestamp));
+        super(source, new IngestDocMetadata(index, id, version, routing, versionType, timestamp));
     }
 
     /**