diff --git a/src/util/config-file.hpp b/src/util/config-file.hpp
index 2bb6c2d..65e4e7d 100644
--- a/src/util/config-file.hpp
+++ b/src/util/config-file.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2013-2016 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).
  *
@@ -52,11 +52,7 @@
   class Error : public std::runtime_error
   {
   public:
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-
-    }
+    using std::runtime_error::runtime_error;
   };
 
   typedef boost::property_tree::ptree Parsed;
diff --git a/src/util/io.hpp b/src/util/io.hpp
index 5a8034a..5d457fc 100644
--- a/src/util/io.hpp
+++ b/src/util/io.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).
  *
@@ -33,11 +33,7 @@
 class Error : public std::runtime_error
 {
 public:
-  explicit
-  Error(const std::string& what)
-    : std::runtime_error(what)
-  {
-  }
+  using std::runtime_error::runtime_error;
 };
 
 /** \brief indicates how a file or stream is encoded
diff --git a/src/util/regex/regex-matcher.hpp b/src/util/regex/regex-matcher.hpp
index bb18a8f..74ef1ce 100644
--- a/src/util/regex/regex-matcher.hpp
+++ b/src/util/regex/regex-matcher.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).
  *
@@ -35,11 +35,7 @@
   class Error : public std::runtime_error
   {
   public:
-    explicit
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-    }
+    using std::runtime_error::runtime_error;
   };
 
   enum RegexExprType {
diff --git a/src/util/sha256.hpp b/src/util/sha256.hpp
index d729e90..7df5ead 100644
--- a/src/util/sha256.hpp
+++ b/src/util/sha256.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).
  *
@@ -47,11 +47,7 @@
   class Error : public std::runtime_error
   {
   public:
-    explicit
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-    }
+    using std::runtime_error::runtime_error;
   };
 
   /**