diff --git a/daemon/face/face-system.hpp b/daemon/face/face-system.hpp
index d7d534b..36148df 100644
--- a/daemon/face/face-system.hpp
+++ b/daemon/face/face-system.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2022,  Regents of the University of California,
+ * Copyright (c) 2014-2023,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -26,7 +26,6 @@
 #ifndef NFD_DAEMON_FACE_FACE_SYSTEM_HPP
 #define NFD_DAEMON_FACE_FACE_SYSTEM_HPP
 
-#include "network-predicate.hpp"
 #include "common/config-file.hpp"
 
 #include <ndn-cxx/net/network-address.hpp>
@@ -62,15 +61,17 @@
   [[nodiscard]] std::set<const ProtocolFactory*>
   listProtocolFactories() const;
 
-  /** \return ProtocolFactory for the specified registered factory id or nullptr if not found.
+  /**
+   * \return ProtocolFactory for the specified registered factory id or nullptr if not found.
    */
   ProtocolFactory*
-  getFactoryById(const std::string& id);
+  getFactoryById(const std::string& id) const;
 
-  /** \return ProtocolFactory for the specified FaceUri scheme or nullptr if not found.
+  /**
+   * \return ProtocolFactory for the specified FaceUri scheme or nullptr if not found.
    */
   ProtocolFactory*
-  getFactoryByScheme(const std::string& scheme);
+  getFactoryByScheme(const std::string& scheme) const;
 
   bool
   hasFactoryForScheme(const std::string& scheme) const;