diff --git a/src/daemon/rrset.hpp b/src/daemon/rrset.hpp
index aaedcfe..0e4b883 100644
--- a/src/daemon/rrset.hpp
+++ b/src/daemon/rrset.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014, Regents of the University of California.
+/*
+ * Copyright (c) 2014-2018, Regents of the University of California.
  *
  * This file is part of NDNS (Named Data Networking Domain Name Service).
  * See AUTHORS.md for complete list of NDNS authors and contributors.
@@ -187,6 +187,9 @@
     return !(*this == other);
   }
 
+  bool
+  operator<(const Rrset& other) const;
+
 private:
   uint64_t m_id;
   Zone* m_zone;