diff --git a/tests/sys_socket_test.cpp b/tests/sys_socket_test.cpp
index 506e01f..0342547 100644
--- a/tests/sys_socket_test.cpp
+++ b/tests/sys_socket_test.cpp
@@ -34,7 +34,7 @@
 static void* ConnectFn(void* data) {
   ConnectData* pdata = reinterpret_cast<ConnectData*>(data);
   bool (*callback_fn)(int) = pdata->callback_fn;
-  void* return_value = NULL;
+  void* return_value = nullptr;
 
   int fd = socket(PF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
   if (fd < 0) {
@@ -52,7 +52,7 @@
     GTEST_LOG_(ERROR) << "connect call failed: " << strerror(errno);
     return_value = reinterpret_cast<void*>(-1);
   }
-  else if (callback_fn != NULL && !callback_fn(fd)) {
+  else if (callback_fn != nullptr && !callback_fn(fd)) {
     return_value = reinterpret_cast<void*>(-1);
   }
 
@@ -79,7 +79,7 @@
   ConnectData connect_data(callback_fn, sock_path);
 
   pthread_t thread;
-  ASSERT_EQ(0, pthread_create(&thread, NULL, ConnectFn, &connect_data));
+  ASSERT_EQ(0, pthread_create(&thread, nullptr, ConnectFn, &connect_data));
 
   fd_set read_set;
   FD_ZERO(&read_set);
@@ -87,19 +87,19 @@
   timeval tv;
   tv.tv_sec = 5;
   tv.tv_usec = 0;
-  ASSERT_LT(0, select(fd+1, &read_set, NULL, NULL, &tv));
+  ASSERT_LT(0, select(fd+1, &read_set, nullptr, nullptr, &tv));
 
   test_fn(&addr, fd);
 
   void* ret_val;
   ASSERT_EQ(0, pthread_join(thread, &ret_val));
-  ASSERT_EQ(NULL, ret_val);
+  ASSERT_EQ(nullptr, ret_val);
 
   close(fd);
 }
 
 TEST(sys_socket, accept4_error) {
-  ASSERT_EQ(-1, accept4(-1, NULL, NULL, 0));
+  ASSERT_EQ(-1, accept4(-1, nullptr, nullptr, 0));
   ASSERT_EQ(EBADF, errno);
 }
 
@@ -115,7 +115,7 @@
 }
 
 TEST(sys_socket, accept4_smoke) {
-  RunTest(TestAccept4, NULL, "test_accept");
+  RunTest(TestAccept4, nullptr, "test_accept");
 }
 
 const char* g_RecvMsgs[] = {
@@ -174,7 +174,7 @@
 }
 
 TEST(sys_socket, recvmmsg_error) {
-  ASSERT_EQ(-1, recvmmsg(-1, NULL, 0, 0, NULL));
+  ASSERT_EQ(-1, recvmmsg(-1, nullptr, 0, 0, nullptr));
   ASSERT_EQ(EBADF, errno);
 }
 
@@ -217,7 +217,7 @@
     timeval tv;
     tv.tv_sec = 5;
     tv.tv_usec = 0;
-    ASSERT_LT(0, select(fd_acc+1, &read_set, NULL, NULL, &tv));
+    ASSERT_LT(0, select(fd_acc+1, &read_set, nullptr, nullptr, &tv));
     char buffer[100];
     ASSERT_EQ(strlen(g_SendMsgs[i]) + 1,
               static_cast<size_t>(recv(fd_acc, buffer, sizeof(buffer), 0)));
@@ -232,6 +232,6 @@
 }
 
 TEST(sys_socket, sendmmsg_error) {
-  ASSERT_EQ(-1, sendmmsg(-1, NULL, 0, 0));
+  ASSERT_EQ(-1, sendmmsg(-1, nullptr, 0, 0));
   ASSERT_EQ(EBADF, errno);
 }