diff --git a/src/main/org/apache/tools/ant/types/optional/depend/ClassfileSet.java b/src/main/org/apache/tools/ant/types/optional/depend/ClassfileSet.java
index 3ff010949..d92bf2855 100644
--- a/src/main/org/apache/tools/ant/types/optional/depend/ClassfileSet.java
+++ b/src/main/org/apache/tools/ant/types/optional/depend/ClassfileSet.java
@@ -156,7 +156,7 @@ public class ClassfileSet extends FileSet {
      * @param root the configured class root.
      */
     public void addConfiguredRoot(ClassRoot root) {
-        rootClasses.add(root.getClassname());    
+        rootClasses.addElement(root.getClassname());    
     }
 
     /**