Index: build.xml
===================================================================
--- build.xml	(revision 712416)
+++ build.xml	(working copy)
@@ -89,7 +89,7 @@
           description="Runs all unit tests (including contribs)"
   />
 
-  <property name="tag" value="lucene_2_4_0"/>
+  <property name="tag" value="${compatibility.tag}"/>
 	
   <path id="tag.test.classpath">
     <path refid="demo.classpath"/>
@@ -110,15 +110,23 @@
 	<sequential>
 	  <mkdir dir="${tags.dir}/${tag}"/>
       <exec dir="${tags.dir}/${tag}" executable="svn"
-            failifexecutionfails="true">
+            failifexecutionfails="false">
         <arg line="checkout http://svn.apache.org/repos/asf/lucene/java/tags/${tag}/src/test/"/>
       </exec>
 	</sequential>
   </target>
+
+  <available
+    property="tag.available"
+  	file="${tags.dir}/${tag}/test"
+  />
 	
   <target name="test-tag" depends="download-tag, compile-core, compile-demo"
   	description="Runs tests of a previous Lucene version. Specify tag version like this: -Dtag=lucene_2_4_0">
 	<sequential>
+	  <fail unless="tag.available">
+	  	Specified tag '${tag}' could not be found in directory '${tags.dir}/${tag}'.
+	  </fail>
 	  <mkdir dir="${build.dir}/${tag}/test"/>
 	  <compile-test-macro srcdir="${tags.dir}/${tag}/test" destdir="${build.dir}/${tag}/classes/test"
 		  				  test.classpath="tag.test.classpath"/>
@@ -353,7 +361,7 @@
      </copy>
   </target>
 
-  <target name="nightly" depends="test, package-tgz, changes-to-html">
+  <target name="nightly" depends="test, test-tag, package-tgz, changes-to-html">
   </target>
 
   <!-- ================================================================== -->
Index: common-build.xml
===================================================================
--- common-build.xml	(revision 712416)
+++ common-build.xml	(working copy)
@@ -41,6 +41,7 @@
   <property name="name" value="${ant.project.name}"/>
   <property name="Name" value="Lucene"/>
   <property name="version" value="2.9-dev"/>
+  <property name="compatibility.tag" value="lucene_2_4_0"/>
   <property name="spec.version" value="${version}"/>	
   <property name="year" value="2000-${current.year}"/>
   <property name="final.name" value="lucene-${name}-${version}"/>