diff --git a/src/handles/watch-handle.cpp b/src/handles/watch-handle.cpp
index bee036f..6fe93d4 100644
--- a/src/handles/watch-handle.cpp
+++ b/src/handles/watch-handle.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2017, Regents of the University of California.
+ * Copyright (c) 2014-2018, Regents of the University of California.
  *
  * This file is part of NDN repo-ng (Next generation of NDN repository).
  * See AUTHORS.md for complete list of repo-ng authors and contributors.
@@ -59,7 +59,7 @@
   try {
     extractParameter(interest, prefix, parameter);
   }
-  catch (RepoCommandParameter::Error) {
+  catch (const RepoCommandParameter::Error&) {
     negativeReply(interest, 403);
     return;
   }
@@ -223,7 +223,7 @@
   try {
     extractParameter(interest, prefix, parameter);
   }
-  catch (RepoCommandParameter::Error) {
+  catch (const RepoCommandParameter::Error&) {
     negativeReply(interest, 403);
     return;
   }
@@ -254,7 +254,7 @@
   try {
     extractParameter(interest, prefix, parameter);
   }
-  catch (RepoCommandParameter::Error) {
+  catch (const RepoCommandParameter::Error&) {
     negativeReply(interest, 403);
     return;
   }