diff --git a/tests/daemon/face/test-netif.cpp b/tests/daemon/face/test-netif.cpp
index b3e6fde..c1a734d 100644
--- a/tests/daemon/face/test-netif.cpp
+++ b/tests/daemon/face/test-netif.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018,  Regents of the University of California,
+ * Copyright (c) 2014-2019,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -33,32 +33,23 @@
 std::vector<shared_ptr<const NetworkInterface>>
 enumerateNetworkInterfaces(NetworkMonitor& netmon)
 {
-  if ((netmon.getCapabilities() & NetworkMonitor::CAP_ENUM) == 0) {
-    BOOST_THROW_EXCEPTION(NetworkMonitor::Error("NetworkMonitor::CAP_ENUM is unavailable"));
+  if (netmon.getCapabilities() & NetworkMonitor::CAP_ENUM) {
+    netmon.onEnumerationCompleted.connect([] { getGlobalIoService().stop(); });
+    getGlobalIoService().run();
+    getGlobalIoService().reset();
   }
-
-  netmon.onEnumerationCompleted.connect([] { getGlobalIoService().stop(); });
-  getGlobalIoService().run();
-  getGlobalIoService().reset();
   return netmon.listNetworkInterfaces();
 }
 
 std::vector<shared_ptr<const NetworkInterface>>
 collectNetworkInterfaces(bool allowCached)
 {
-  using ndn::net::NetworkMonitor;
-
-  static std::vector<shared_ptr<const NetworkInterface>> cached;
-  // cached.empty() indicates there's no cached list of netifs.
-  // Although it could also mean a system without any network interface, this situation is rare
-  // because the loopback interface is present on almost all systems.
-
-  if (!allowCached || cached.empty()) {
+  static optional<std::vector<shared_ptr<const NetworkInterface>>> cached;
+  if (!allowCached || !cached) {
     NetworkMonitor netmon(getGlobalIoService());
     cached = enumerateNetworkInterfaces(netmon);
   }
-
-  return cached;
+  return *cached;
 }
 
 } // namespace tests
diff --git a/tests/daemon/face/test-netif.hpp b/tests/daemon/face/test-netif.hpp
index 7c926e6..42820dd 100644
--- a/tests/daemon/face/test-netif.hpp
+++ b/tests/daemon/face/test-netif.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018,  Regents of the University of California,
+ * Copyright (c) 2014-2019,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -43,8 +43,7 @@
 /** \brief Enumerate network interfaces using the given NetworkMonitor
  *  \param netmon a NetworkMonitor constructed on the global io_service.
  *  \note This function is blocking
- *  \warning Signals are supported if caller keeps NetworkMonitor running
- *  \throw ndn::net::NetworkMonitor::Error NetworkMonitor::CAP_ENUM is unavailable
+ *  \note Signals are supported if caller keeps \p netmon running
  */
 std::vector<shared_ptr<const NetworkInterface>>
 enumerateNetworkInterfaces(NetworkMonitor& netmon);
@@ -53,7 +52,6 @@
  *  \param allowCached if true, previously collected information can be returned
  *  \note This function is blocking if \p allowCached is false or no previous information exists
  *  \warning Signals are not triggered on returned NetworkInterfaces because NetworkMonitor is not running
- *  \throw ndn::net::NetworkMonitor::Error NetworkMonitor::CAP_ENUM is unavailable
  */
 std::vector<shared_ptr<const NetworkInterface>>
 collectNetworkInterfaces(bool allowCached = true);