diff --git a/libc/bionic/locale.cpp b/libc/bionic/locale.cpp
index e20a1de..4fade84 100644
--- a/libc/bionic/locale.cpp
+++ b/libc/bionic/locale.cpp
@@ -30,45 +30,127 @@
 #include <pthread.h>
 #include <stdlib.h>
 
-static pthread_once_t locale_once = PTHREAD_ONCE_INIT;
-static lconv locale;
+// We currently support a single locale, the "C" locale (also known as "POSIX").
+
+struct __locale_t {
+  // Because we only support one locale, these are just tokens with no data.
+};
+
+static pthread_once_t gLocaleOnce = PTHREAD_ONCE_INIT;
+static lconv gLocale;
+
+static pthread_once_t gUselocaleKeyOnce = PTHREAD_ONCE_INIT;
+static pthread_key_t gUselocaleKey;
 
 static void __locale_init() {
-  locale.decimal_point = const_cast<char*>(".");
+  gLocale.decimal_point = const_cast<char*>(".");
 
   char* not_available = const_cast<char*>("");
-  locale.thousands_sep = not_available;
-  locale.grouping = not_available;
-  locale.int_curr_symbol = not_available;
-  locale.currency_symbol = not_available;
-  locale.mon_decimal_point = not_available;
-  locale.mon_thousands_sep = not_available;
-  locale.mon_grouping = not_available;
-  locale.positive_sign = not_available;
-  locale.negative_sign = not_available;
+  gLocale.thousands_sep = not_available;
+  gLocale.grouping = not_available;
+  gLocale.int_curr_symbol = not_available;
+  gLocale.currency_symbol = not_available;
+  gLocale.mon_decimal_point = not_available;
+  gLocale.mon_thousands_sep = not_available;
+  gLocale.mon_grouping = not_available;
+  gLocale.positive_sign = not_available;
+  gLocale.negative_sign = not_available;
 
-  locale.int_frac_digits = CHAR_MAX;
-  locale.frac_digits = CHAR_MAX;
-  locale.p_cs_precedes = CHAR_MAX;
-  locale.p_sep_by_space = CHAR_MAX;
-  locale.n_cs_precedes = CHAR_MAX;
-  locale.n_sep_by_space = CHAR_MAX;
-  locale.p_sign_posn = CHAR_MAX;
-  locale.n_sign_posn = CHAR_MAX;
-  locale.int_p_cs_precedes = CHAR_MAX;
-  locale.int_p_sep_by_space = CHAR_MAX;
-  locale.int_n_cs_precedes = CHAR_MAX;
-  locale.int_n_sep_by_space = CHAR_MAX;
-  locale.int_p_sign_posn = CHAR_MAX;
-  locale.int_n_sign_posn = CHAR_MAX;
+  gLocale.int_frac_digits = CHAR_MAX;
+  gLocale.frac_digits = CHAR_MAX;
+  gLocale.p_cs_precedes = CHAR_MAX;
+  gLocale.p_sep_by_space = CHAR_MAX;
+  gLocale.n_cs_precedes = CHAR_MAX;
+  gLocale.n_sep_by_space = CHAR_MAX;
+  gLocale.p_sign_posn = CHAR_MAX;
+  gLocale.n_sign_posn = CHAR_MAX;
+  gLocale.int_p_cs_precedes = CHAR_MAX;
+  gLocale.int_p_sep_by_space = CHAR_MAX;
+  gLocale.int_n_cs_precedes = CHAR_MAX;
+  gLocale.int_n_sep_by_space = CHAR_MAX;
+  gLocale.int_p_sign_posn = CHAR_MAX;
+  gLocale.int_n_sign_posn = CHAR_MAX;
+}
+
+static void __uselocale_key_init() {
+  pthread_key_create(&gUselocaleKey, NULL);
+}
+
+static bool __is_supported_locale(const char* locale) {
+  return (strcmp(locale, "") == 0 || strcmp(locale, "C") == 0 || strcmp(locale, "POSIX") == 0);
+}
+
+static locale_t __new_locale() {
+  return reinterpret_cast<locale_t>(malloc(sizeof(__locale_t)));
 }
 
 lconv* localeconv() {
-  pthread_once(&locale_once, __locale_init);
-  return &locale;
+  pthread_once(&gLocaleOnce, __locale_init);
+  return &gLocale;
 }
 
-// setlocale(3) always fails on bionic.
-char* setlocale(int /*category*/, char const* /*locale*/) {
+locale_t duplocale(locale_t l) {
+  locale_t clone = __new_locale();
+  if (clone != NULL && l != LC_GLOBAL_LOCALE) {
+    *clone = *l;
+  }
+  return clone;
+}
+
+void freelocale(locale_t l) {
+  free(l);
+}
+
+locale_t newlocale(int category_mask, const char* locale_name, locale_t /*base*/) {
+  // Is 'category_mask' valid?
+  if ((category_mask & ~LC_ALL_MASK) != 0) {
+    errno = EINVAL;
+    return NULL;
+  }
+
+  if (!__is_supported_locale(locale_name)) {
+    errno = ENOENT;
+    return NULL;
+  }
+
+  return __new_locale();
+}
+
+char* setlocale(int category, char const* locale_name) {
+  // Is 'category' valid?
+  if (category < LC_CTYPE || category > LC_IDENTIFICATION) {
+    errno = EINVAL;
+    return NULL;
+  }
+
+  // Caller just wants to query the current locale?
+  if (locale_name == NULL) {
+    return const_cast<char*>("C");
+  }
+
+  // Caller wants one of the mandatory POSIX locales?
+  if (__is_supported_locale(locale_name)) {
+    return const_cast<char*>("C");
+  }
+
+  // We don't support any other locales.
+  errno = ENOENT;
   return NULL;
 }
+
+locale_t uselocale(locale_t new_locale) {
+  pthread_once(&gUselocaleKeyOnce, __uselocale_key_init);
+
+  locale_t old_locale = static_cast<locale_t>(pthread_getspecific(gUselocaleKey));
+
+  // If this is the first call to uselocale(3) on this thread, we return LC_GLOBAL_LOCALE.
+  if (old_locale == NULL) {
+    old_locale = LC_GLOBAL_LOCALE;
+  }
+
+  if (new_locale != NULL) {
+    pthread_setspecific(gUselocaleKey, new_locale);
+  }
+
+  return old_locale;
+}