diff --git a/CHANGES.txt b/CHANGES.txt
index d945996001..7354c4cec0 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -207,6 +207,9 @@ Trunk (unreleased changes)
     HADOOP-6549. TestDoAsEffectiveUser should use ip address of the host
      for superuser ip check(jnp via boryas)
 
+    HADOOP-6570. RPC#stopProxy throws NPE if getProxyEngine(proxy) returns
+    null. (hairong)
+
 Release 0.21.0 - Unreleased
 
   INCOMPATIBLE CHANGES
diff --git a/src/java/org/apache/hadoop/ipc/RPC.java b/src/java/org/apache/hadoop/ipc/RPC.java
index 906d526075..36874c511d 100644
--- a/src/java/org/apache/hadoop/ipc/RPC.java
+++ b/src/java/org/apache/hadoop/ipc/RPC.java
@@ -244,8 +244,9 @@ public static Object getProxy(Class protocol, long clientVersion,
    * @param proxy the proxy to be stopped
    */
   public static void stopProxy(Object proxy) {
-    if (proxy!=null) {
-      getProxyEngine(proxy).stopProxy(proxy);
+    RpcEngine rpcEngine;
+    if (proxy!=null && (rpcEngine = getProxyEngine(proxy)) != null) {
+      rpcEngine.stopProxy(proxy);
     }
   }
 
diff --git a/src/test/core/org/apache/hadoop/ipc/TestRPC.java b/src/test/core/org/apache/hadoop/ipc/TestRPC.java
index b4fd02631c..0bb3f8dc5c 100644
--- a/src/test/core/org/apache/hadoop/ipc/TestRPC.java
+++ b/src/test/core/org/apache/hadoop/ipc/TestRPC.java
@@ -39,6 +39,8 @@
 import org.apache.hadoop.security.authorize.Service;
 import org.apache.hadoop.security.authorize.ServiceAuthorizationManager;
 
+import static org.mockito.Mockito.*;
+
 /** Unit tests for RPC. */
 public class TestRPC extends TestCase {
   private static final String ADDRESS = "0.0.0.0";
@@ -392,6 +394,14 @@ public void testNoPings() throws Exception {
     conf.setBoolean("ipc.client.ping", false);
     new TestRPC("testnoPings").testCalls(conf);
   }
+
+  /**
+   * Test stopping a non-registered proxy
+   * @throws Exception
+   */
+  public void testStopNonRegisteredProxy() throws Exception {
+    RPC.stopProxy(mock(TestProtocol.class));
+  }
   
   public static void main(String[] args) throws Exception {