diff -r 1c999569643b -r acf2c31e22d4 samples/reentrant/src/org/apidesign/reentrant/CriticalSectionReentrantImmutable.java
--- a/samples/reentrant/src/org/apidesign/reentrant/CriticalSectionReentrantImmutable.java	Sat Jun 14 10:04:51 2008 +0200
+++ b/samples/reentrant/src/org/apidesign/reentrant/CriticalSectionReentrantImmutable.java	Sat Jun 14 10:04:53 2008 +0200
@@ -13,7 +13,10 @@
     // BEGIN: reentrant.merge.immutable
     public int sumBigger(Collection<T> args) {
         for (;;) {
-            ImmutableData<T> previous = this.data;
+            ImmutableData<T> previous;
+            synchronized (this) {
+                previous = this.data;
+            }
             int[] ret = { 0 };
             ImmutableData<T> now = doCriticalSection(args, previous, ret);