diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index a119850cd808e..09026cbe1e4b8 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -285,6 +285,7 @@ endif()
 
 # Feature options -------------------------------------------------------------
 option(LIBCXX_HAS_MUSL_LIBC "Build libc++ with support for the Musl C library" OFF)
+option(LIBCXX_HAS_NEWLIB_LIBC "Build libc++ with support for the Newlib C library" OFF)
 option(LIBCXX_HAS_PTHREAD_API "Ignore auto-detection and force use of pthread API" OFF)
 option(LIBCXX_HAS_WIN32_THREAD_API "Ignore auto-detection and force use of win32 thread API" OFF)
 option(LIBCXX_HAS_EXTERNAL_THREAD_API
@@ -741,6 +742,7 @@ config_define(${LIBCXX_HAS_PTHREAD_API} _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define(${LIBCXX_HAS_EXTERNAL_THREAD_API} _LIBCPP_HAS_THREAD_API_EXTERNAL)
 config_define(${LIBCXX_HAS_WIN32_THREAD_API} _LIBCPP_HAS_THREAD_API_WIN32)
 config_define(${LIBCXX_HAS_MUSL_LIBC} _LIBCPP_HAS_MUSL_LIBC)
+config_define(${LIBCXX_HAS_NEWLIB_LIBC} _LIBCPP_HAS_NEWLIB_LIBC)
 config_define_if(LIBCXX_NO_VCRUNTIME _LIBCPP_NO_VCRUNTIME)
 config_define(${LIBCXX_ENABLE_FILESYSTEM} _LIBCPP_HAS_FILESYSTEM)
 config_define(${LIBCXX_ENABLE_RANDOM_DEVICE} _LIBCPP_HAS_RANDOM_DEVICE)
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 131ba99357d62..4870f050709de 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -533,6 +533,7 @@ set(files
   __locale_dir/support/fuchsia.h
   __locale_dir/support/linux.h
   __locale_dir/support/netbsd.h
+  __locale_dir/support/newlib.h
   __locale_dir/support/no_locale/characters.h
   __locale_dir/support/no_locale/strtonum.h
   __locale_dir/support/windows.h
diff --git a/libcxx/include/__config_site.in b/libcxx/include/__config_site.in
index b68c0c8258366..0f8e83d87c9c5 100644
--- a/libcxx/include/__config_site.in
+++ b/libcxx/include/__config_site.in
@@ -17,6 +17,7 @@
 #cmakedefine01 _LIBCPP_HAS_MONOTONIC_CLOCK
 #cmakedefine01 _LIBCPP_HAS_TERMINAL
 #cmakedefine01 _LIBCPP_HAS_MUSL_LIBC
+#cmakedefine01 _LIBCPP_HAS_NEWLIB_LIBC
 #cmakedefine01 _LIBCPP_HAS_THREAD_API_PTHREAD
 #cmakedefine01 _LIBCPP_HAS_THREAD_API_EXTERNAL
 #cmakedefine01 _LIBCPP_HAS_THREAD_API_WIN32
diff --git a/libcxx/include/__locale_dir/locale_base_api.h b/libcxx/include/__locale_dir/locale_base_api.h
index 8c8f00061d1ed..f83af881db215 100644
--- a/libcxx/include/__locale_dir/locale_base_api.h
+++ b/libcxx/include/__locale_dir/locale_base_api.h
@@ -123,6 +123,8 @@
 #    include <__locale_dir/support/fuchsia.h>
 #  elif defined(__linux__)
 #    include <__locale_dir/support/linux.h>
+#  elif _LIBCPP_HAS_NEWLIB_LIBC
+#    include <__locale_dir/support/newlib.h>
 #  else
 
 // TODO: This is a temporary definition to bridge between the old way we defined the locale base API
diff --git a/libcxx/include/__locale_dir/support/newlib.h b/libcxx/include/__locale_dir/support/newlib.h
new file mode 100644
index 0000000000000..eaac1031dd33f
--- /dev/null
+++ b/libcxx/include/__locale_dir/support/newlib.h
@@ -0,0 +1,269 @@
+//===-----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___LOCALE_DIR_SUPPORT_NEWLIB_H
+#define _LIBCPP___LOCALE_DIR_SUPPORT_NEWLIB_H
+
+#include <__config>
+#include <clocale>
+#include <cstdio>
+#include <cstdlib>
+#include <ctype.h>
+#include <stdarg.h>
+#include <string.h>
+#include <time.h>
+#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  include <cwchar>
+#  include <wctype.h>
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+namespace __locale {
+
+struct __locale_guard {
+  _LIBCPP_HIDE_FROM_ABI __locale_guard(locale_t& __loc) : __old_loc_(::uselocale(__loc)) {}
+
+  _LIBCPP_HIDE_FROM_ABI ~__locale_guard() {
+    if (__old_loc_)
+      ::uselocale(__old_loc_);
+  }
+
+  locale_t __old_loc_;
+
+  __locale_guard(__locale_guard const&)            = delete;
+  __locale_guard& operator=(__locale_guard const&) = delete;
+};
+
+//
+// Locale management
+//
+
+using __locale_t _LIBCPP_NODEBUG = locale_t;
+using __lconv_t _LIBCPP_NODEBUG  = lconv;
+
+inline _LIBCPP_HIDE_FROM_ABI __locale_t __newlocale(int __category_mask, const char* __locale, __locale_t __base) {
+  return ::newlocale(__category_mask, __locale, __base);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI void __freelocale(__locale_t __loc) { ::freelocale(__loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI char* __setlocale(int __category, char const* __locale) {
+  return ::setlocale(__category, __locale);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI __lconv_t* __localeconv(__locale_t& __loc) {
+  __locale_guard __current(__loc);
+  return std::localeconv();
+}
+
+#define _LIBCPP_COLLATE_MASK LC_COLLATE_MASK
+#define _LIBCPP_CTYPE_MASK LC_CTYPE_MASK
+#define _LIBCPP_MONETARY_MASK LC_MONETARY_MASK
+#define _LIBCPP_NUMERIC_MASK LC_NUMERIC_MASK
+#define _LIBCPP_TIME_MASK LC_TIME_MASK
+#define _LIBCPP_MESSAGES_MASK LC_MESSAGES_MASK
+#define _LIBCPP_ALL_MASK LC_ALL_MASK
+#define _LIBCPP_LC_ALL LC_ALL
+
+//
+// Strtonum functions
+//
+
+inline _LIBCPP_HIDE_FROM_ABI float __strtof(const char* __nptr, char** __endptr, __locale_t __loc) {
+  return ::strtof_l(__nptr, __endptr, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI double __strtod(const char* __nptr, char** __endptr, __locale_t __loc) {
+  return ::strtod_l(__nptr, __endptr, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI long double __strtold(const char* __nptr, char** __endptr, __locale_t __loc) {
+  return ::strtold_l(__nptr, __endptr, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI long long __strtoll(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
+  return ::strtoll_l(__nptr, __endptr, __base, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI unsigned long long
+__strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
+  return ::strtoull_l(__nptr, __endptr, __base, __loc);
+}
+
+//
+// Character manipulation functions
+//
+
+inline _LIBCPP_HIDE_FROM_ABI int __isdigit(int __c, __locale_t __loc) { return isdigit_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __isxdigit(int __c, __locale_t __loc) { return isxdigit_l(__c, __loc); }
+
+#if defined(_LIBCPP_BUILDING_LIBRARY)
+inline _LIBCPP_HIDE_FROM_ABI int __toupper(int __c, __locale_t __loc) { return toupper_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __tolower(int __c, __locale_t __loc) { return tolower_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __strcoll(const char* __s1, const char* __s2, __locale_t __loc) {
+  return strcoll_l(__s1, __s2, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t __strxfrm(char* __dest, const char* __src, size_t __n, __locale_t __loc) {
+  return strxfrm_l(__dest, __src, __n, __loc);
+}
+
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
+inline _LIBCPP_HIDE_FROM_ABI int __iswctype(wint_t __c, wctype_t __type, __locale_t __loc) {
+  return iswctype_l(__c, __type, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswspace(wint_t __c, __locale_t __loc) { return iswspace_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswprint(wint_t __c, __locale_t __loc) { return iswprint_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswcntrl(wint_t __c, __locale_t __loc) { return iswcntrl_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswupper(wint_t __c, __locale_t __loc) { return iswupper_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswlower(wint_t __c, __locale_t __loc) { return iswlower_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswalpha(wint_t __c, __locale_t __loc) { return iswalpha_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswblank(wint_t __c, __locale_t __loc) { return iswblank_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswdigit(wint_t __c, __locale_t __loc) { return iswdigit_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswpunct(wint_t __c, __locale_t __loc) { return iswpunct_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __iswxdigit(wint_t __c, __locale_t __loc) { return iswxdigit_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI wint_t __towupper(wint_t __c, __locale_t __loc) { return towupper_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI wint_t __towlower(wint_t __c, __locale_t __loc) { return towlower_l(__c, __loc); }
+
+inline _LIBCPP_HIDE_FROM_ABI int __wcscoll(const wchar_t* __ws1, const wchar_t* __ws2, __locale_t __loc) {
+  return wcscoll_l(__ws1, __ws2, __loc);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t __wcsxfrm(wchar_t* __dest, const wchar_t* __src, size_t __n, __locale_t __loc) {
+  return wcsxfrm_l(__dest, __src, __n, __loc);
+}
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
+
+inline _LIBCPP_HIDE_FROM_ABI
+size_t __strftime(char* __s, size_t __max, const char* __format, const struct tm* __tm, __locale_t __loc) {
+  return strftime_l(__s, __max, __format, __tm, __loc);
+}
+
+//
+// Other functions
+//
+
+inline _LIBCPP_HIDE_FROM_ABI decltype(MB_CUR_MAX) __mb_len_max(__locale_t __loc) {
+  __locale_guard __current(__loc);
+  return MB_CUR_MAX;
+}
+
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
+inline _LIBCPP_HIDE_FROM_ABI wint_t __btowc(int __c, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::btowc(__c);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI int __wctob(wint_t __c, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::wctob(__c);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t
+__wcsnrtombs(char* __dest, const wchar_t** __src, size_t __nwc, size_t __len, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return ::wcsnrtombs(__dest, __src, __nwc, __len, __ps); // non-standard
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t __wcrtomb(char* __s, wchar_t __wc, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::wcrtomb(__s, __wc, __ps);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t
+__mbsnrtowcs(wchar_t* __dest, const char** __src, size_t __nms, size_t __len, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return ::mbsnrtowcs(__dest, __src, __nms, __len, __ps); // non-standard
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t
+__mbrtowc(wchar_t* __pwc, const char* __s, size_t __n, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::mbrtowc(__pwc, __s, __n, __ps);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI int __mbtowc(wchar_t* __pwc, const char* __pmb, size_t __max, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::mbtowc(__pwc, __pmb, __max);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t __mbrlen(const char* __s, size_t __n, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::mbrlen(__s, __n, __ps);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI size_t
+__mbsrtowcs(wchar_t* __dest, const char** __src, size_t __len, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return std::mbsrtowcs(__dest, __src, __len, __ps);
+}
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#endif   // _LIBCPP_BUILDING_LIBRARY
+
+#ifndef _LIBCPP_COMPILER_GCC // GCC complains that this can't be always_inline due to C-style varargs
+_LIBCPP_HIDE_FROM_ABI
+#endif
+inline _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 4, 5) int __snprintf(
+    char* __s, size_t __n, __locale_t __loc, const char* __format, ...) {
+  va_list __va;
+  va_start(__va, __format);
+  __locale_guard __current(__loc);
+  int __res = std::vsnprintf(__s, __n, __format, __va);
+  va_end(__va);
+  return __res;
+}
+
+#ifndef _LIBCPP_COMPILER_GCC // GCC complains that this can't be always_inline due to C-style varargs
+_LIBCPP_HIDE_FROM_ABI
+#endif
+inline _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 3, 4) int __asprintf(
+    char** __s, __locale_t __loc, const char* __format, ...) {
+  va_list __va;
+  va_start(__va, __format);
+  __locale_guard __current(__loc);
+  int __res = ::vasprintf(__s, __format, __va); // non-standard
+  va_end(__va);
+  return __res;
+}
+
+#ifndef _LIBCPP_COMPILER_GCC // GCC complains that this can't be always_inline due to C-style varargs
+_LIBCPP_HIDE_FROM_ABI
+#endif
+inline _LIBCPP_ATTRIBUTE_FORMAT(__scanf__, 3, 4) int __sscanf(
+    const char* __s, __locale_t __loc, const char* __format, ...) {
+  va_list __va;
+  va_start(__va, __format);
+  __locale_guard __current(__loc);
+  int __res = std::vsscanf(__s, __format, __va);
+  va_end(__va);
+  return __res;
+}
+
+} // namespace __locale
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___LOCALE_DIR_SUPPORT_NEWLIB_H
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index 7ca57f6455dd8..f547e33a17dc8 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -1591,6 +1591,7 @@ module std [system] {
       textual header "__locale_dir/support/fuchsia.h"
       textual header "__locale_dir/support/linux.h"
       textual header "__locale_dir/support/netbsd.h"
+      textual header "__locale_dir/support/newlib.h"
       textual header "__locale_dir/support/no_locale/characters.h"
       textual header "__locale_dir/support/no_locale/strtonum.h"
       textual header "__locale_dir/support/windows.h"