diff --git a/docs/tuning.md b/docs/tuning.md
index cbf37213aa724b9f8a41f0aba8af0bf3f1f85c3b..9c43b315bbb9e7b7ce9b4ad65b87285ba977f99d 100644
--- a/docs/tuning.md
+++ b/docs/tuning.md
@@ -45,6 +45,7 @@ and calling `conf.set("spark.serializer", "org.apache.spark.serializer.KryoSeria
 This setting configures the serializer used for not only shuffling data between worker
 nodes but also when serializing RDDs to disk.  The only reason Kryo is not the default is because of the custom
 registration requirement, but we recommend trying it in any network-intensive application.
+Since Spark 2.0.0, we internally use Kryo serializer when shuffling RDDs with simple types, arrays of simple types, or string type.
 
 Spark automatically includes Kryo serializers for the many commonly-used core Scala classes covered
 in the AllScalaRegistrar from the [Twitter chill](https://github.com/twitter/chill) library.