--- old/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/ObjectSynchronizer.java	2017-08-09 15:48:30.240351630 +0900
+++ new/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/ObjectSynchronizer.java	2017-08-09 15:48:30.138349458 +0900
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2014, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -108,13 +108,16 @@
 
     public Object next() {
       Address addr;
-      if (index > 0) {
-        addr = blockAddr.addOffsetTo(index*objectMonitorTypeSize);
-      } else {
+      if (index == 0) {
+        // advance to next block
         blockAddr = block.freeNext();
+        if (blockAddr == null) {
+          throw new NoSuchElementException();
+        }
+        block = new ObjectMonitor(blockAddr);
         index = blockSize - 1;
-        addr = blockAddr.addOffsetTo(index*objectMonitorTypeSize);
       }
+      addr = blockAddr.addOffsetTo(index*objectMonitorTypeSize);
       index --;
       return new ObjectMonitor(addr);
     }