diff --git a/ndn-cpp/encoding/binary-xml-element-reader.hpp b/ndn-cpp/encoding/binary-xml-element-reader.hpp
index 36342ab..ef0f9a2 100644
--- a/ndn-cpp/encoding/binary-xml-element-reader.hpp
+++ b/ndn-cpp/encoding/binary-xml-element-reader.hpp
@@ -27,7 +27,7 @@
    * later, you must copy.
    * @param elementLength length of element
    */
-  virtual void onReceivedElement(unsigned char *element, unsigned int elementLength) = 0;
+  virtual void onReceivedElement(const unsigned char *element, unsigned int elementLength) = 0;
   
 private:
   /**
diff --git a/ndn-cpp/node.cpp b/ndn-cpp/node.cpp
index b8773fc..8a46384 100644
--- a/ndn-cpp/node.cpp
+++ b/ndn-cpp/node.cpp
@@ -97,7 +97,7 @@
   }
 }
 
-void Node::onReceivedElement(unsigned char *element, unsigned int elementLength)
+void Node::onReceivedElement(const unsigned char *element, unsigned int elementLength)
 {
   BinaryXmlDecoder decoder(element, elementLength);
   
diff --git a/ndn-cpp/node.hpp b/ndn-cpp/node.hpp
index a7e5548..461fe26 100644
--- a/ndn-cpp/node.hpp
+++ b/ndn-cpp/node.hpp
@@ -78,7 +78,7 @@
   
   const ptr_lib::shared_ptr<Transport> &getTransport() { return transport_; }
   
-  virtual void onReceivedElement(unsigned char *element, unsigned int elementLength);
+  void onReceivedElement(const unsigned char *element, unsigned int elementLength);
   
   void shutdown();