diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index cf6d4153cd..7236052f6c 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -330,6 +330,9 @@ Release 2.0.5-beta - UNRELEASED
     MAPREDUCE-5066. Added a timeout for the job.end.notification.url. (Ivan
     Mitic via acmurthy)
 
+    MAPREDUCE-5146. application classloader may be used too early to load
+    classes. (Sangjin Lee via tomwhite)
+
 Release 2.0.4-alpha - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapred/YarnChild.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapred/YarnChild.java
index 33ff626df3..27847889d7 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapred/YarnChild.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapred/YarnChild.java
@@ -20,10 +20,8 @@ package org.apache.hadoop.mapred;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.io.PrintStream;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.security.PrivilegedExceptionAction;
@@ -148,6 +146,9 @@ class YarnChild {
       // Add tokens to new user so that it may execute its task correctly.
       childUGI.addCredentials(credentials);
 
+      // set job classloader if configured before invoking the task
+      MRApps.setJobClassLoader(job);
+
       // Create a final reference to the task for the doAs block
       final Task taskFinal = task;
       childUGI.doAs(new PrivilegedExceptionAction<Object>() {
@@ -255,9 +256,6 @@ class YarnChild {
     final JobConf job = new JobConf(MRJobConfig.JOB_CONF_FILE);
     job.setCredentials(credentials);
 
-    // set job classloader if configured
-    MRApps.setJobClassLoader(job);
-
     String appAttemptIdEnv = System
         .getenv(MRJobConfig.APPLICATION_ATTEMPT_ID_ENV);
     LOG.debug("APPLICATION_ATTEMPT_ID: " + appAttemptIdEnv);