diff --git a/src/key-locator.hpp b/src/key-locator.hpp
index 8c206e4..b442854 100644
--- a/src/key-locator.hpp
+++ b/src/key-locator.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).
  *
@@ -162,6 +162,9 @@
   mutable Block m_wire;
 };
 
+std::ostream&
+operator<<(std::ostream& os, const KeyLocator& keyLocator);
+
 } // namespace ndn
 
 #endif // NDN_KEY_LOCATOR_HPP