diff --git a/tests/stdlib_test.cpp b/tests/stdlib_test.cpp
index 2fbd937..6e41555 100644
--- a/tests/stdlib_test.cpp
+++ b/tests/stdlib_test.cpp
@@ -281,35 +281,35 @@
 TEST(stdlib, realpath__NULL_filename) {
   errno = 0;
   // Work around the compile-time error generated by FORTIFY here.
-  const char* path = NULL;
-  char* p = realpath(path, NULL);
-  ASSERT_TRUE(p == NULL);
+  const char* path = nullptr;
+  char* p = realpath(path, nullptr);
+  ASSERT_TRUE(p == nullptr);
   ASSERT_EQ(EINVAL, errno);
 }
 
 TEST(stdlib, realpath__empty_filename) {
   errno = 0;
-  char* p = realpath("", NULL);
-  ASSERT_TRUE(p == NULL);
+  char* p = realpath("", nullptr);
+  ASSERT_TRUE(p == nullptr);
   ASSERT_EQ(ENOENT, errno);
 }
 
 TEST(stdlib, realpath__ENOENT) {
   errno = 0;
-  char* p = realpath("/this/directory/path/almost/certainly/does/not/exist", NULL);
-  ASSERT_TRUE(p == NULL);
+  char* p = realpath("/this/directory/path/almost/certainly/does/not/exist", nullptr);
+  ASSERT_TRUE(p == nullptr);
   ASSERT_EQ(ENOENT, errno);
 }
 
 TEST(stdlib, realpath__component_after_non_directory) {
   errno = 0;
-  char* p = realpath("/dev/null/.", NULL);
-  ASSERT_TRUE(p == NULL);
+  char* p = realpath("/dev/null/.", nullptr);
+  ASSERT_TRUE(p == nullptr);
   ASSERT_EQ(ENOTDIR, errno);
 
   errno = 0;
-  p = realpath("/dev/null/..", NULL);
-  ASSERT_TRUE(p == NULL);
+  p = realpath("/dev/null/..", nullptr);
+  ASSERT_TRUE(p == nullptr);
   ASSERT_EQ(ENOTDIR, errno);
 }
 
@@ -324,7 +324,7 @@
   char* p = realpath("/proc/self/exe", buf);
   ASSERT_STREQ(executable_path, p);
 
-  p = realpath("/proc/self/exe", NULL);
+  p = realpath("/proc/self/exe", nullptr);
   ASSERT_STREQ(executable_path, p);
   free(p);
 }
@@ -354,18 +354,18 @@
 
 static void* TestBug57421_child(void* arg) {
   pthread_t main_thread = reinterpret_cast<pthread_t>(arg);
-  pthread_join(main_thread, NULL);
+  pthread_join(main_thread, nullptr);
   char* value = getenv("ENVIRONMENT_VARIABLE");
-  if (value == NULL) {
+  if (value == nullptr) {
     setenv("ENVIRONMENT_VARIABLE", "value", 1);
   }
-  return NULL;
+  return nullptr;
 }
 
 static void TestBug57421_main() {
   pthread_t t;
-  ASSERT_EQ(0, pthread_create(&t, NULL, TestBug57421_child, reinterpret_cast<void*>(pthread_self())));
-  pthread_exit(NULL);
+  ASSERT_EQ(0, pthread_create(&t, nullptr, TestBug57421_child, reinterpret_cast<void*>(pthread_self())));
+  pthread_exit(nullptr);
 }
 
 // Even though this isn't really a death test, we have to say "DeathTest" here so gtest knows to
@@ -483,20 +483,20 @@
 }
 
 TEST(stdlib, strtof_2206701) {
-  ASSERT_EQ(0.0f, strtof("7.0064923216240853546186479164495e-46", NULL));
-  ASSERT_EQ(1.4e-45f, strtof("7.0064923216240853546186479164496e-46", NULL));
+  ASSERT_EQ(0.0f, strtof("7.0064923216240853546186479164495e-46", nullptr));
+  ASSERT_EQ(1.4e-45f, strtof("7.0064923216240853546186479164496e-46", nullptr));
 }
 
 TEST(stdlib, strtod_largest_subnormal) {
   // This value has been known to cause javac and java to infinite loop.
   // http://www.exploringbinary.com/java-hangs-when-converting-2-2250738585072012e-308/
-  ASSERT_EQ(2.2250738585072014e-308, strtod("2.2250738585072012e-308", NULL));
-  ASSERT_EQ(2.2250738585072014e-308, strtod("0.00022250738585072012e-304", NULL));
-  ASSERT_EQ(2.2250738585072014e-308, strtod("00000002.2250738585072012e-308", NULL));
-  ASSERT_EQ(2.2250738585072014e-308, strtod("2.225073858507201200000e-308", NULL));
-  ASSERT_EQ(2.2250738585072014e-308, strtod("2.2250738585072012e-00308", NULL));
-  ASSERT_EQ(2.2250738585072014e-308, strtod("2.22507385850720129978001e-308", NULL));
-  ASSERT_EQ(-2.2250738585072014e-308, strtod("-2.2250738585072012e-308", NULL));
+  ASSERT_EQ(2.2250738585072014e-308, strtod("2.2250738585072012e-308", nullptr));
+  ASSERT_EQ(2.2250738585072014e-308, strtod("0.00022250738585072012e-304", nullptr));
+  ASSERT_EQ(2.2250738585072014e-308, strtod("00000002.2250738585072012e-308", nullptr));
+  ASSERT_EQ(2.2250738585072014e-308, strtod("2.225073858507201200000e-308", nullptr));
+  ASSERT_EQ(2.2250738585072014e-308, strtod("2.2250738585072012e-00308", nullptr));
+  ASSERT_EQ(2.2250738585072014e-308, strtod("2.22507385850720129978001e-308", nullptr));
+  ASSERT_EQ(-2.2250738585072014e-308, strtod("-2.2250738585072012e-308", nullptr));
 }
 
 TEST(stdlib, quick_exit) {
@@ -584,7 +584,7 @@
   int fd = getpt();
   ASSERT_NE(-1, fd);
   errno = 0;
-  char* buf = NULL;
+  char* buf = nullptr;
   ASSERT_EQ(EINVAL, ptsname_r(fd, buf, 128));
   ASSERT_EQ(EINVAL, errno);
   close(fd);
@@ -635,7 +635,7 @@
   int fd = getpt();
   ASSERT_NE(-1, fd);
   errno = 0;
-  char* buf = NULL;
+  char* buf = nullptr;
   ASSERT_EQ(EINVAL, ttyname_r(fd, buf, 128));
   ASSERT_EQ(EINVAL, errno);
   close(fd);