diff --git a/src/adjacent.hpp b/src/adjacent.hpp
index 1e6eac5..72a8d98 100644
--- a/src/adjacent.hpp
+++ b/src/adjacent.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2017,  The University of Memphis,
+ * Copyright (c) 2014-2018,  The University of Memphis,
  *                           Regents of the University of California
  *
  * This file is part of NLSR (Named-data Link State Routing).
@@ -140,19 +140,19 @@
   operator<(const Adjacent& adjacent) const;
 
   inline bool
-  compare(const ndn::Name& adjacencyName)
+  compare(const ndn::Name& adjacencyName) const
   {
     return m_name == adjacencyName;
   }
 
   inline bool
-  compareFaceId(const uint64_t faceId)
+  compareFaceId(const uint64_t faceId) const
   {
     return m_faceId == faceId;
   }
 
   inline bool
-  compareFaceUri(const ndn::FaceUri& faceUri)
+  compareFaceUri(const ndn::FaceUri& faceUri) const
   {
     return m_faceUri == faceUri;
   }