diff --git a/src/net/dns.hpp b/src/net/dns.hpp
index 961e5bd..9357613 100644
--- a/src/net/dns.hpp
+++ b/src/net/dns.hpp
@@ -60,13 +60,10 @@
   }
 };
 
-struct Error : public std::runtime_error
+class Error : public std::runtime_error
 {
-  explicit
-  Error(const std::string& what)
-    : std::runtime_error(what)
-  {
-  }
+public:
+  using std::runtime_error::runtime_error;
 };
 
 typedef function<void (const IpAddress& address)> SuccessCallback;
diff --git a/src/net/network-monitor.hpp b/src/net/network-monitor.hpp
index 2441e3e..afafd58 100644
--- a/src/net/network-monitor.hpp
+++ b/src/net/network-monitor.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).
  *
@@ -53,11 +53,7 @@
   class Error : public std::runtime_error
   {
   public:
-    explicit
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-    }
+    using std::runtime_error::runtime_error;
   };
 
   /**