diff --git a/src/etc/testcases/taskdefs/available.xml b/src/etc/testcases/taskdefs/available.xml
index 453d573c5..57dbc6f9d 100644
--- a/src/etc/testcases/taskdefs/available.xml
+++ b/src/etc/testcases/taskdefs/available.xml
@@ -75,7 +75,7 @@
 
   <target name="test15">
     <available property="test" 
-               classname=""/>
+               classname="org.apache.tools.ant.taskdefs.this_class_does_not_exist"/>
   </target>
 
 </project>
diff --git a/src/main/org/apache/tools/ant/taskdefs/Available.java b/src/main/org/apache/tools/ant/taskdefs/Available.java
index d0e9132e1..ae77885dc 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Available.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Available.java
@@ -103,7 +103,9 @@ public class Available extends Task {
     }
 
     public void setClassname(String classname) {
-        this.classname = classname;
+        if (!"".equals(classname)) {
+            this.classname = classname;
+        }
     }
 
     public void setFile(File file) {