diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index e8f329102d..21b5f79616 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -281,6 +281,9 @@ Release 2.1.1-beta - UNRELEASED
 
   IMPROVEMENTS
 
+    HDFS-4513. Clarify in the WebHDFS REST API that all JSON respsonses may
+    contain additional properties.  (szetszwo)
+
   OPTIMIZATIONS
 
   BUG FIXES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/WebHDFS.apt.vm b/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/WebHDFS.apt.vm
index 7735f8dafe..71063c3a69 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/WebHDFS.apt.vm
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/WebHDFS.apt.vm
@@ -185,6 +185,10 @@ curl -i --negotiate -u : "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=..."
 curl -i "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?delegation=<TOKEN>&op=..."
 +---------------------------------
 
+  []
+ 
+  See also: {{{../hadoop-common/HttpAuthentication.html}Authentication for Hadoop HTTP web-consoles}}
+
 * {Proxy Users}
 
   When the proxy user feature is enabled, a proxy user <P> may submit a request on behalf of another user <U>.
@@ -971,6 +975,12 @@ Transfer-Encoding: chunked
   See {{{http://tools.ietf.org/id/draft-zyp-json-schema-03.html}draft-zyp-json-schema-03}}
   for the syntax definitions of the JSON schemas.
 
+  <<Note>> that the default value of
+  {{{http://tools.ietf.org/id/draft-zyp-json-schema-03.html#additionalProperties}<<<additionalProperties>>>}}
+  is an empty schema which allows any value for additional properties.
+  Therefore, all WebHDFS JSON responses allow any additional property.
+  However, if additional properties are included in the responses, they are
+  considered as optional properties in order to maintain compatibility.
 
 ** {Boolean JSON Schema}