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:
   /**