diff --git a/src/main/org/apache/tools/ant/types/AbstractFileSet.java b/src/main/org/apache/tools/ant/types/AbstractFileSet.java
index 9ccc1d0d9..0fed2ee58 100644
--- a/src/main/org/apache/tools/ant/types/AbstractFileSet.java
+++ b/src/main/org/apache/tools/ant/types/AbstractFileSet.java
@@ -210,7 +210,7 @@ public abstract class AbstractFileSet extends DataType
      * @param file the single <code>File</code> included in this
      *             <code>AbstractFileSet</code>.
      */
-    public void setFile(File file) {
+    public synchronized void setFile(File file) {
         if (isReference()) {
             throw tooManyAttributes();
         }