diff --git a/tests/unit-tests/security/test-certificate-cache.cpp b/tests/unit-tests/security/test-certificate-cache.cpp
index d98dd4a..54454e1 100644
--- a/tests/unit-tests/security/test-certificate-cache.cpp
+++ b/tests/unit-tests/security/test-certificate-cache.cpp
@@ -110,6 +110,7 @@
 BOOST_FIXTURE_TEST_CASE(TtlRefresh, UnitTestTimeFixture)
 {
   cache->insertCertificate(cert1); // 500ms
+
   io.poll();
   BOOST_CHECK_EQUAL(cache->getSize(), 1);
 
@@ -119,6 +120,7 @@
 
     // Refresh certificate in cache
   cache->insertCertificate(cert1); // +500ms
+
   io.poll();
   BOOST_CHECK_EQUAL(cache->getSize(), 1);
 
@@ -140,6 +142,7 @@
   BOOST_CHECK_EQUAL(cache->getSize(), 2);
 
   cache->reset();
+
   io.poll();
   BOOST_CHECK_EQUAL(cache->getSize(), 0);
 }
diff --git a/tests/unit-tests/util/test-time-unit-test-clock.cpp b/tests/unit-tests/util/test-time-unit-test-clock.cpp
index f9b121d..e43d4ed 100644
--- a/tests/unit-tests/util/test-time-unit-test-clock.cpp
+++ b/tests/unit-tests/util/test-time-unit-test-clock.cpp
@@ -24,6 +24,7 @@
 
 #include "boost-test.hpp"
 #include <boost/lexical_cast.hpp>
+#include <thread>
 
 namespace ndn {
 namespace tests {
@@ -54,7 +55,8 @@
 {
   BOOST_CHECK_EQUAL(time::system_clock::now().time_since_epoch(),
                     time::UnitTestClockTraits<time::system_clock>::getDefaultStartTime());
-  usleep(1000000);
+  std::this_thread::sleep_for(std::chrono::milliseconds(100));
+
   BOOST_CHECK_EQUAL(time::system_clock::now().time_since_epoch(),
                     time::UnitTestClockTraits<time::system_clock>::getDefaultStartTime());
 
@@ -109,7 +111,7 @@
   BOOST_CHECK_EQUAL(time::steady_clock::now().time_since_epoch(),
                     time::steady_clock::duration::zero());
 
-  usleep(1000000);
+  std::this_thread::sleep_for(std::chrono::milliseconds(100));
   BOOST_CHECK_EQUAL(time::steady_clock::now().time_since_epoch(),
                     time::steady_clock::duration::zero());
 
@@ -138,13 +140,12 @@
   bool hasFired = false;
   scheduler.scheduleEvent(time::seconds(100), [&] { hasFired = true; });
 
-  for (size_t i = 0; i < 10; ++i)
-    io.poll();
+  io.poll();
   BOOST_CHECK_EQUAL(hasFired, false);
 
   steadyClock->advance(time::seconds(100));
-  for (size_t i = 0; i < 10; ++i)
-    io.poll();
+
+  io.poll();
   BOOST_CHECK_EQUAL(hasFired, true);
 }