diff --git a/src/Nest/Modules/Indices/Fielddata/String/StringFielddataFormat.cs b/src/Nest/Modules/Indices/Fielddata/String/StringFielddataFormat.cs
index f427a9799c5..6b5c3a4e0da 100644
--- a/src/Nest/Modules/Indices/Fielddata/String/StringFielddataFormat.cs
+++ b/src/Nest/Modules/Indices/Fielddata/String/StringFielddataFormat.cs
@@ -1,4 +1,5 @@
-using System.Runtime.Serialization;
+using System;
+using System.Runtime.Serialization;
 
 namespace Nest
 {
@@ -6,6 +7,7 @@ public enum StringFielddataFormat
 	{
 		[EnumMember(Value = "paged_bytes")]
 		PagedBytes,
+		[Obsolete("Deprecated in 2.0, will be removed in next major version release")]
 		[EnumMember(Value = "doc_values")]
 		DocValues,
 		[EnumMember(Value = "disabled")]