diff --git a/libs/core/src/main/java/org/opensearch/core/index/Index.java b/libs/core/src/main/java/org/opensearch/core/index/Index.java
index 750725c24bcb0..b5ee482bcd952 100644
--- a/libs/core/src/main/java/org/opensearch/core/index/Index.java
+++ b/libs/core/src/main/java/org/opensearch/core/index/Index.java
@@ -59,7 +59,7 @@ public class Index implements Writeable, ToXContentObject {
     public static final Index[] EMPTY_ARRAY = new Index[0];
     private static final String INDEX_UUID_KEY = "index_uuid";
     private static final String INDEX_NAME_KEY = "index_name";
-    public static final String UNKNOWN_INDEX_NAME = "unknown";
+    public static final String UNKNOWN_INDEX_NAME = "_unknown_";
 
     private static final ObjectParser<Builder, Void> INDEX_PARSER = new ObjectParser<>("index", Builder::new);
     static {