diff --git a/src/security/v2/certificate-cache.hpp b/src/security/v2/certificate-cache.hpp
index a5109a8..53157b4 100644
--- a/src/security/v2/certificate-cache.hpp
+++ b/src/security/v2/certificate-cache.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2017 Regents of the University of California.
+ * Copyright (c) 2013-2018 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -118,7 +118,7 @@
   refresh();
 
 public:
-  static const time::nanoseconds&
+  static time::nanoseconds
   getDefaultLifetime();
 
 private: