diff --git a/src/Nest/CommonOptions/Sorting/SortFormatter.cs b/src/Nest/CommonOptions/Sorting/SortFormatter.cs
index 6facc57664d..336b5c84fee 100644
--- a/src/Nest/CommonOptions/Sorting/SortFormatter.cs
+++ b/src/Nest/CommonOptions/Sorting/SortFormatter.cs
@@ -75,7 +75,10 @@ public ISort Deserialize(ref JsonReader reader, IJsonFormatterResolver formatter
 		public void Serialize(ref JsonWriter writer, ISort value, IJsonFormatterResolver formatterResolver)
 		{
 			if (value?.SortKey == null)
+			{
+				writer.WriteNull();
 				return;
+			}
 
 			writer.WriteBeginObject();
 			var settings = formatterResolver.GetConnectionSettings();