diff --git a/src/encoding/tlv.hpp b/src/encoding/tlv.hpp
index ad964e2..c9a6520 100644
--- a/src/encoding/tlv.hpp
+++ b/src/encoding/tlv.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2013-2015 Regents of the University of California.
+ * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -99,6 +99,9 @@
   SignatureSha256WithEcdsa = 3
 };
 
+std::ostream&
+operator<<(std::ostream& os, const SignatureTypeValue& signatureType);
+
 /** @brief TLV codes for SignatureInfo features
  *  @sa docs/tutorials/certificate-format.rst
  */