diff --git a/hadoop-yarn-project/CHANGES.txt b/hadoop-yarn-project/CHANGES.txt
index 2aae75e636e..75dbaf75ec1 100644
--- a/hadoop-yarn-project/CHANGES.txt
+++ b/hadoop-yarn-project/CHANGES.txt
@@ -360,6 +360,9 @@ Release 2.7.0 - UNRELEASED
     YARN-2933. Capacity Scheduler preemption policy should only consider capacity 
     without labels temporarily. (Mayank Bansal via wangda)
 
+    YARN-2731. Fixed RegisterApplicationMasterResponsePBImpl to properly invoke 
+    maybeInitBuilder. (Carlo Curino via wangda)
+
 Release 2.6.0 - 2014-11-18
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/api/protocolrecords/impl/pb/RegisterApplicationMasterResponsePBImpl.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/api/protocolrecords/impl/pb/RegisterApplicationMasterResponsePBImpl.java
index 32dc85d6f38..a95aadfbef8 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/api/protocolrecords/impl/pb/RegisterApplicationMasterResponsePBImpl.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/api/protocolrecords/impl/pb/RegisterApplicationMasterResponsePBImpl.java
@@ -229,11 +229,11 @@ public class RegisterApplicationMasterResponsePBImpl extends
   
   @Override
   public void setClientToAMTokenMasterKey(ByteBuffer key) {
+    maybeInitBuilder();
     if (key == null) {
       builder.clearClientToAmTokenMasterKey();
       return;
     }
-    maybeInitBuilder();
     builder.setClientToAmTokenMasterKey(ByteString.copyFrom(key));
   }
   
@@ -316,6 +316,7 @@ public class RegisterApplicationMasterResponsePBImpl extends
   
   @Override
   public void setNMTokensFromPreviousAttempts(final List<NMToken> nmTokens) {
+    maybeInitBuilder();
     if (nmTokens == null || nmTokens.isEmpty()) {
       if (this.nmTokens != null) {
         this.nmTokens.clear();