diff --git a/src/main/org/apache/tools/ant/types/resources/Resources.java b/src/main/org/apache/tools/ant/types/resources/Resources.java
index 16719f8ed..629dde4df 100644
--- a/src/main/org/apache/tools/ant/types/resources/Resources.java
+++ b/src/main/org/apache/tools/ant/types/resources/Resources.java
@@ -122,7 +122,7 @@ public class Resources extends DataType implements ResourceCollection {
             rc = new Vector();
         }
         rc.add(c);
-        FailFast.invalidate(this);
+        invalidateExistingIterators();
         coll = null;
         setChecked(false);
     }
@@ -215,6 +215,13 @@ public class Resources extends DataType implements ResourceCollection {
         }
     }
 
+    /**
+     * Allow subclasses to notify existing Iterators they have experienced concurrent modification.
+     */
+    protected void invalidateExistingIterators() {
+        FailFast.invalidate(this);
+    }
+
     /**
      * Resolves references, allowing any ResourceCollection.
      * @return the referenced ResourceCollection.