--- old/agent/src/share/classes/sun/jvm/hotspot/oops/OopField.java	Fri Mar 18 14:59:17 2011
+++ new/agent/src/share/classes/sun/jvm/hotspot/oops/OopField.java	Fri Mar 18 14:59:17 2011
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2002, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2011, 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
@@ -41,11 +41,17 @@
   }
 
   public Oop getValue(Oop obj) {
+    if (!isVMField() && !obj.isInstance() && !obj.isArray()) {
+      throw new InternalError();
+    }
     return obj.getHeap().newOop(getValueAsOopHandle(obj));
   }
 
   /** Debugging support */
   public OopHandle getValueAsOopHandle(Oop obj) {
+    if (!isVMField() && !obj.isInstance() && !obj.isArray()) {
+      throw new InternalError(obj.toString());
+    }
     return obj.getHandle().getOopHandleAt(getOffset());
   }