diff --git a/src/etc/testcases/taskdefs/length.xml b/src/etc/testcases/taskdefs/length.xml
index 226393742..e9faf919a 100644
--- a/src/etc/testcases/taskdefs/length.xml
+++ b/src/etc/testcases/taskdefs/length.xml
@@ -104,6 +104,18 @@
     <length string="foo" file="${ant.file}" />
   </target>
 
+  <target name="testImmutable">
+    <length string="foo" property="length.string" />
+    <length string="foobar" property="length.string" />
+    <fail>
+      <condition>
+        <not>
+          <equals arg1="3" arg2="${length.string}" />
+        </not>
+      </condition>
+    </fail>
+  </target>
+
   <target name="cleanup">
     <delete dir="${dir}" />
   </target>
diff --git a/src/main/org/apache/tools/ant/taskdefs/Length.java b/src/main/org/apache/tools/ant/taskdefs/Length.java
index 8d514a8ae..32ea48268 100755
--- a/src/main/org/apache/tools/ant/taskdefs/Length.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Length.java
@@ -190,7 +190,8 @@ public class Length extends Task {
 
     private class PropertyOutputStream extends ByteArrayOutputStream {
         public void close() {
-            getProject().setProperty(property, new String(toByteArray()).trim());
+            getProject().setNewProperty(
+                property, new String(toByteArray()).trim());
         }
     }
 
diff --git a/src/testcases/org/apache/tools/ant/taskdefs/LengthTest.java b/src/testcases/org/apache/tools/ant/taskdefs/LengthTest.java
index 143cf2788..d9470125c 100755
--- a/src/testcases/org/apache/tools/ant/taskdefs/LengthTest.java
+++ b/src/testcases/org/apache/tools/ant/taskdefs/LengthTest.java
@@ -67,4 +67,8 @@ public class LengthTest extends BuildFileTest {
             "should fail", "string length function only");
     }
 
+    public void testImmutable() {
+        executeTarget("testImmutable");
+    }
+
 }