diff --git a/tests/unit-tests/security/tpm/back-end-wrapper-file.hpp b/tests/unit-tests/security/tpm/back-end-wrapper-file.hpp
index 64f5a0a..dabd6d3 100644
--- a/tests/unit-tests/security/tpm/back-end-wrapper-file.hpp
+++ b/tests/unit-tests/security/tpm/back-end-wrapper-file.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).
  *
@@ -54,7 +54,7 @@
   }
 
   std::string
-  getScheme()
+  getScheme() const
   {
     return "tpm-file";
   }