diff --git a/src/main/java/rx/internal/operators/BufferUntilSubscriber.java b/src/main/java/rx/internal/operators/BufferUntilSubscriber.java
index 737b8d2bee..e4722c9a60 100644
--- a/src/main/java/rx/internal/operators/BufferUntilSubscriber.java
+++ b/src/main/java/rx/internal/operators/BufferUntilSubscriber.java
@@ -70,7 +70,7 @@ boolean casObserverRef(Observer<? super T>  expected, Observer<? super T>  next)
             return OBSERVER_UPDATER.compareAndSet(this, expected, next);
         }
 
-        Object guard = new Object();
+        final Object guard = new Object();
         /* protected by guard */
         boolean emitting = false;