diff --git a/core/java/src/net/i2p/util/ConcurrentHashSet.java b/core/java/src/net/i2p/util/ConcurrentHashSet.java
index 3610c54b9..6c6d8bfb6 100644
--- a/core/java/src/net/i2p/util/ConcurrentHashSet.java
+++ b/core/java/src/net/i2p/util/ConcurrentHashSet.java
@@ -14,7 +14,7 @@ import java.util.concurrent.ConcurrentHashMap;
  */
 public class ConcurrentHashSet<E> extends AbstractSet<E> implements Set<E> {
     private static final Object DUMMY = new Object();
-    private Map<E, Object> _map;
+    private final Map<E, Object> _map;
 
     public ConcurrentHashSet() {
         _map = new ConcurrentHashMap();