diff --git a/CHANGES.txt b/CHANGES.txt
index bfc25ce960..8dcbcb97f7 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -868,6 +868,9 @@ Trunk (unreleased changes)
     HADOOP-6114. Fix javadoc documentation for FileStatus.getLen.
     (Dmitry Rzhevskiy via dhruba)
 
+    HADOOP-6131. A sysproperty should not be set unless the property 
+    is set on the ant command line in build.xml (hong tang via mahadev)
+
 Release 0.20.1 - Unreleased
 
   INCOMPATIBLE CHANGES
diff --git a/build.xml b/build.xml
index 8d97576603..9aec9f62f2 100644
--- a/build.xml
+++ b/build.xml
@@ -507,8 +507,10 @@
       <sysproperty key="java.library.path"
        value="${build.native}/lib:${lib.dir}/native/${build.platform}"/>
       <sysproperty key="install.c++.examples" value="${install.c++.examples}"/>
-      <sysproperty key="io.compression.codec.lzo.class"
-		  value="${io.compression.codec.lzo.class}"/>
+      <!-- set io.compression.codec.lzo.class in the child jvm only if it is set -->
+      <syspropertyset dynamic="no">
+         <propertyref name="io.compression.codec.lzo.class"/>
+      </syspropertyset>
       <!-- set compile.c++ in the child jvm only if it is set -->
       <syspropertyset dynamic="no">
          <propertyref name="compile.c++"/>