diff --git a/tests/locale_test.cpp b/tests/locale_test.cpp
index 8b38c40..b4da6de 100644
--- a/tests/locale_test.cpp
+++ b/tests/locale_test.cpp
@@ -48,14 +48,14 @@
 }
 
 TEST(locale, setlocale) {
-  EXPECT_STREQ("C.UTF-8", setlocale(LC_ALL, NULL));
-  EXPECT_STREQ("C.UTF-8", setlocale(LC_CTYPE, NULL));
+  EXPECT_STREQ("C.UTF-8", setlocale(LC_ALL, nullptr));
+  EXPECT_STREQ("C.UTF-8", setlocale(LC_CTYPE, nullptr));
 
   errno = 0;
-  EXPECT_EQ(NULL, setlocale(-1, NULL));
+  EXPECT_EQ(nullptr, setlocale(-1, nullptr));
   EXPECT_EQ(EINVAL, errno);
   errno = 0;
-  EXPECT_EQ(NULL, setlocale(13, NULL));
+  EXPECT_EQ(nullptr, setlocale(13, nullptr));
   EXPECT_EQ(EINVAL, errno);
 
 #if defined(__BIONIC__)
@@ -68,53 +68,53 @@
   EXPECT_STREQ("C", setlocale(LC_ALL, "POSIX"));
 
   errno = 0;
-  EXPECT_EQ(NULL, setlocale(LC_ALL, "this-is-not-a-locale"));
+  EXPECT_EQ(nullptr, setlocale(LC_ALL, "this-is-not-a-locale"));
   EXPECT_EQ(ENOENT, errno); // POSIX specified, not an implementation detail!
 }
 
 TEST(locale, newlocale_invalid_category_mask) {
   errno = 0;
-  EXPECT_EQ(0, newlocale(1 << 20, "C", 0));
+  EXPECT_EQ(nullptr, newlocale(1 << 20, "C", nullptr));
   EXPECT_EQ(EINVAL, errno);
 }
 
 TEST(locale, newlocale_NULL_locale_name) {
   errno = 0;
-  EXPECT_EQ(0, newlocale(LC_ALL, NULL, 0));
+  EXPECT_EQ(nullptr, newlocale(LC_ALL, nullptr, nullptr));
   EXPECT_EQ(EINVAL, errno);
 }
 
 TEST(locale, newlocale_bad_locale_name) {
   errno = 0;
-  EXPECT_EQ(0, newlocale(LC_ALL, "this-is-not-a-locale", 0));
+  EXPECT_EQ(nullptr, newlocale(LC_ALL, "this-is-not-a-locale", nullptr));
   EXPECT_EQ(ENOENT, errno); // POSIX specified, not an implementation detail!
 }
 
 TEST(locale, newlocale) {
-  locale_t l = newlocale(LC_ALL, "C", 0);
-  ASSERT_TRUE(l != NULL);
+  locale_t l = newlocale(LC_ALL, "C", nullptr);
+  ASSERT_TRUE(l != nullptr);
   freelocale(l);
 }
 
 TEST(locale, duplocale) {
   locale_t cloned_global = duplocale(LC_GLOBAL_LOCALE);
-  ASSERT_TRUE(cloned_global != NULL);
+  ASSERT_TRUE(cloned_global != nullptr);
   freelocale(cloned_global);
 }
 
 TEST(locale, uselocale) {
-  locale_t original = uselocale(NULL);
-  EXPECT_FALSE(original == 0);
+  locale_t original = uselocale(nullptr);
+  EXPECT_FALSE(original == nullptr);
   EXPECT_EQ(LC_GLOBAL_LOCALE, original);
 
-  locale_t n = newlocale(LC_ALL, "C", 0);
-  EXPECT_FALSE(n == 0);
+  locale_t n = newlocale(LC_ALL, "C", nullptr);
+  EXPECT_FALSE(n == nullptr);
   EXPECT_FALSE(n == original);
 
   locale_t old = uselocale(n);
   EXPECT_TRUE(old == original);
 
-  EXPECT_EQ(n, uselocale(NULL));
+  EXPECT_EQ(n, uselocale(nullptr));
 }
 
 TEST(locale, mb_cur_max) {
@@ -122,8 +122,8 @@
   // initial program conditions because (unless we're the only test that was
   // run), another test has almost certainly called uselocale(3) in this thread.
   // See b/16685652.
-  locale_t cloc = newlocale(LC_ALL, "C", 0);
-  locale_t cloc_utf8 = newlocale(LC_ALL, "C.UTF-8", 0);
+  locale_t cloc = newlocale(LC_ALL, "C", nullptr);
+  locale_t cloc_utf8 = newlocale(LC_ALL, "C.UTF-8", nullptr);
 
   locale_t old_locale = uselocale(cloc);
   ASSERT_EQ(1U, MB_CUR_MAX);