diff --git a/helper/ccnb-parser/visitors/non-negative-integer-visitor.cc b/helper/ccnb-parser/visitors/non-negative-integer-visitor.cc
new file mode 100644
index 0000000..d5fc041
--- /dev/null
+++ b/helper/ccnb-parser/visitors/non-negative-integer-visitor.cc
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2011 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+#include "non-negative-integer-visitor.h"
+
+#include "../syntax-tree/blob.h"
+#include "../syntax-tree/udata.h"
+#include <sstream>
+
+namespace ns3 {
+namespace ndn {
+namespace CcnbParser {
+
+boost::any
+NonNegativeIntegerVisitor::visit (Blob &n) //to throw parsing error
+{
+  // Buffer n.m_blob;
+  throw CcnbDecodingException ();
+}
+
+boost::any
+NonNegativeIntegerVisitor::visit (Udata &n)
+{
+  // std::string n.m_udata;
+  std::istringstream is (n.m_udata);
+  int32_t value;
+  is >> value;
+  if (value<0) // value should be non-negative
+    throw CcnbDecodingException ();
+
+  return static_cast<uint32_t> (value);
+}
+
+}
+}
+}