diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index bc08e62364ff..4ca7653026e4 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -533,7 +533,6 @@ set(files
   __locale_dir/locale_base_api.h
   __locale_dir/locale_base_api/bsd_locale_fallbacks.h
   __locale_dir/locale_base_api/ibm.h
-  __locale_dir/locale_base_api/openbsd.h
   __locale_dir/messages.h
   __locale_dir/money.h
   __locale_dir/num.h
@@ -552,6 +551,7 @@ set(files
   __locale_dir/support/no_locale/conversions.h
   __locale_dir/support/no_locale/formatting.h
   __locale_dir/support/no_locale/strtonum.h
+  __locale_dir/support/openbsd.h
   __locale_dir/support/windows.h
   __locale_dir/time.h
   __locale_dir/wbuffer_convert.h
@@ -782,7 +782,6 @@ set(files
   __support/ibm/locale_mgmt_zos.h
   __support/ibm/nanosleep.h
   __support/xlocale/__posix_l_fallback.h
-  __support/xlocale/__strtonum_fallback.h
   __system_error/errc.h
   __system_error/error_category.h
   __system_error/error_code.h
diff --git a/libcxx/include/__locale_dir/locale_base_api.h b/libcxx/include/__locale_dir/locale_base_api.h
index 60d064cbd7ba..e1e60e18fd7c 100644
--- a/libcxx/include/__locale_dir/locale_base_api.h
+++ b/libcxx/include/__locale_dir/locale_base_api.h
@@ -112,6 +112,8 @@
 #    include <__locale_dir/support/freebsd.h>
 #  elif defined(__NetBSD__)
 #    include <__locale_dir/support/netbsd.h>
+#  elif defined(__OpenBSD__)
+#    include <__locale_dir/support/openbsd.h>
 #  elif defined(_LIBCPP_MSVCRT_LIKE)
 #    include <__locale_dir/support/windows.h>
 #  elif defined(__Fuchsia__)
@@ -130,11 +132,7 @@
 //       (by providing global non-reserved names) and the new API. As we move individual platforms
 //       towards the new way of defining the locale base API, this should disappear since each platform
 //       will define those directly.
-#    if defined(__MVS__)
-#      include <__locale_dir/locale_base_api/ibm.h>
-#    elif defined(__OpenBSD__)
-#      include <__locale_dir/locale_base_api/openbsd.h>
-#    endif
+#    include <__locale_dir/locale_base_api/ibm.h>
 
 #    include <__locale_dir/locale_base_api/bsd_locale_fallbacks.h>
 
diff --git a/libcxx/include/__locale_dir/locale_base_api/openbsd.h b/libcxx/include/__locale_dir/locale_base_api/openbsd.h
deleted file mode 100644
index d4fb224e0c80..000000000000
--- a/libcxx/include/__locale_dir/locale_base_api/openbsd.h
+++ /dev/null
@@ -1,19 +0,0 @@
-// -*- C++ -*-
-//===-----------------------------------------------------------------------===//
-//
-// 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_LOCALE_BASE_API_OPENBSD_H
-#define _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_OPENBSD_H
-
-#include <__support/xlocale/__strtonum_fallback.h>
-#include <clocale>
-#include <cstdlib>
-#include <ctype.h>
-#include <cwctype>
-
-#endif // _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_OPENBSD_H
diff --git a/libcxx/include/__locale_dir/support/openbsd.h b/libcxx/include/__locale_dir/support/openbsd.h
new file mode 100644
index 000000000000..0ec5b12f2ebd
--- /dev/null
+++ b/libcxx/include/__locale_dir/support/openbsd.h
@@ -0,0 +1,229 @@
+// -*- C++ -*-
+//===-----------------------------------------------------------------------===//
+//
+// 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_LOCALE_BASE_API_OPENBSD_H
+#define _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_OPENBSD_H
+
+#include <__config>
+#include <__cstddef/size_t.h>
+#include <__std_mbstate_t.h>
+#include <__utility/forward.h>
+#include <clocale> // std::lconv
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#if _LIBCPP_HAS_WIDE_CHARACTERS
+#  include <wchar.h>
+#  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 {
+  __locale_guard(locale_t& __loc) : __old_loc_(::uselocale(__loc)) {}
+
+  ~__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
+//
+#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
+
+using __locale_t _LIBCPP_NODEBUG = ::locale_t;
+#if defined(_LIBCPP_BUILDING_LIBRARY)
+using __lconv_t _LIBCPP_NODEBUG = std::lconv;
+
+inline __locale_t __newlocale(int __category_mask, const char* __locale, __locale_t __base) {
+  return ::newlocale(__category_mask, __locale, __base);
+}
+
+inline void __freelocale(__locale_t __loc) { ::freelocale(__loc); }
+
+inline char* __setlocale(int __category, char const* __locale) { return ::setlocale(__category, __locale); }
+
+inline __lconv_t* __localeconv(__locale_t& __loc) {
+  __locale_guard __current(__loc);
+  return ::localeconv();
+}
+#endif // _LIBCPP_BUILDING_LIBRARY
+
+//
+// Strtonum functions
+//
+inline float __strtof(const char* __nptr, char** __endptr, __locale_t) { return ::strtof(__nptr, __endptr); }
+
+inline double __strtod(const char* __nptr, char** __endptr, __locale_t) { return ::strtod(__nptr, __endptr); }
+
+inline long double __strtold(const char* __nptr, char** __endptr, __locale_t) { return ::strtold(__nptr, __endptr); }
+
+//
+// Character manipulation functions
+//
+#if defined(_LIBCPP_BUILDING_LIBRARY)
+inline int __toupper(int __c, __locale_t __loc) { return ::toupper_l(__c, __loc); }
+
+inline int __tolower(int __c, __locale_t __loc) { return ::tolower_l(__c, __loc); }
+
+inline int __strcoll(const char* __s1, const char* __s2, __locale_t __loc) { return ::strcoll_l(__s1, __s2, __loc); }
+
+inline 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 int __iswctype(wint_t __c, wctype_t __type, __locale_t __loc) { return ::iswctype_l(__c, __type, __loc); }
+
+inline int __iswspace(wint_t __c, __locale_t __loc) { return ::iswspace_l(__c, __loc); }
+
+inline int __iswprint(wint_t __c, __locale_t __loc) { return ::iswprint_l(__c, __loc); }
+
+inline int __iswcntrl(wint_t __c, __locale_t __loc) { return ::iswcntrl_l(__c, __loc); }
+
+inline int __iswupper(wint_t __c, __locale_t __loc) { return ::iswupper_l(__c, __loc); }
+
+inline int __iswlower(wint_t __c, __locale_t __loc) { return ::iswlower_l(__c, __loc); }
+
+inline int __iswalpha(wint_t __c, __locale_t __loc) { return ::iswalpha_l(__c, __loc); }
+
+inline int __iswblank(wint_t __c, __locale_t __loc) { return ::iswblank_l(__c, __loc); }
+
+inline int __iswdigit(wint_t __c, __locale_t __loc) { return ::iswdigit_l(__c, __loc); }
+
+inline int __iswpunct(wint_t __c, __locale_t __loc) { return ::iswpunct_l(__c, __loc); }
+
+inline int __iswxdigit(wint_t __c, __locale_t __loc) { return ::iswxdigit_l(__c, __loc); }
+
+inline wint_t __towupper(wint_t __c, __locale_t __loc) { return ::towupper_l(__c, __loc); }
+
+inline wint_t __towlower(wint_t __c, __locale_t __loc) { return ::towlower_l(__c, __loc); }
+
+inline int __wcscoll(const wchar_t* __ws1, const wchar_t* __ws2, __locale_t __loc) {
+  return ::wcscoll_l(__ws1, __ws2, __loc);
+}
+
+inline 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_ATTRIBUTE_FORMAT(__strftime__, 3, 0) 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 decltype(MB_CUR_MAX) __mb_len_max(__locale_t __loc) {
+  __locale_guard __current(__loc);
+  return MB_CUR_MAX;
+}
+
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
+inline wint_t __btowc(int __c, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return btowc(__c);
+}
+
+inline int __wctob(wint_t __c, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return wctob(__c);
+}
+
+inline 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); // wcsnrtombs is a POSIX extension
+}
+
+inline size_t __wcrtomb(char* __s, wchar_t __wc, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return wcrtomb(__s, __wc, __ps);
+}
+
+inline 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); // mbsnrtowcs is a POSIX extension
+}
+
+inline size_t __mbrtowc(wchar_t* __pwc, const char* __s, size_t __n, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return mbrtowc(__pwc, __s, __n, __ps);
+}
+
+inline int __mbtowc(wchar_t* __pwc, const char* __pmb, size_t __max, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return mbtowc(__pwc, __pmb, __max);
+}
+
+inline size_t __mbrlen(const char* __s, size_t __n, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return mbrlen(__s, __n, __ps);
+}
+
+inline size_t __mbsrtowcs(wchar_t* __dest, const char** __src, size_t __len, mbstate_t* __ps, __locale_t __loc) {
+  __locale_guard __current(__loc);
+  return mbsrtowcs(__dest, __src, __len, __ps);
+}
+#  endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#endif   // _LIBCPP_BUILDING_LIBRARY
+
+_LIBCPP_DIAGNOSTIC_PUSH
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wgcc-compat")
+_LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wformat-nonliteral") // GCC doesn't support [[gnu::format]] on variadic templates
+#ifdef _LIBCPP_COMPILER_CLANG_BASED
+#  define _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(...) _LIBCPP_ATTRIBUTE_FORMAT(__VA_ARGS__)
+#else
+#  define _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(...) /* nothing */
+#endif
+
+template <class... _Args>
+_LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(__printf__, 4, 5)
+int __snprintf(char* __s, size_t __n, __locale_t __loc, const char* __format, _Args&&... __args) {
+  __locale_guard __current(__loc);
+  return ::snprintf(__s, __n, __format, std::forward<_Args>(__args)...);
+}
+
+template <class... _Args>
+_LIBCPP_VARIADIC_ATTRIBUTE_FORMAT(__printf__, 3, 4)
+int __asprintf(char** __s, __locale_t __loc, const char* __format, _Args&&... __args) {
+  __locale_guard __current(__loc);
+  return ::asprintf(__s, __format, std::forward<_Args>(__args)...); // non-standard
+}
+_LIBCPP_DIAGNOSTIC_POP
+#undef _LIBCPP_VARIADIC_ATTRIBUTE_FORMAT
+
+} // namespace __locale
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___LOCALE_DIR_LOCALE_BASE_API_OPENBSD_H
diff --git a/libcxx/include/__support/xlocale/__strtonum_fallback.h b/libcxx/include/__support/xlocale/__strtonum_fallback.h
deleted file mode 100644
index 90bd59d36c24..000000000000
--- a/libcxx/include/__support/xlocale/__strtonum_fallback.h
+++ /dev/null
@@ -1,37 +0,0 @@
-// -*- C++ -*-
-//===-----------------------------------------------------------------------===//
-//
-// 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
-//
-//===----------------------------------------------------------------------===//
-// These are reimplementations of some extended locale functions ( *_l ) that
-// aren't part of POSIX.  They are widely available though (GLIBC, BSD, maybe
-// others).  The unifying aspect in this case is that all of these functions
-// convert strings to some numeric type.
-//===----------------------------------------------------------------------===//
-
-#ifndef _LIBCPP___SUPPORT_XLOCALE_STRTONUM_FALLBACK_H
-#define _LIBCPP___SUPPORT_XLOCALE_STRTONUM_FALLBACK_H
-
-#include <__config>
-#include <stdlib.h>
-
-#if _LIBCPP_HAS_WIDE_CHARACTERS
-#  include <wchar.h>
-#endif
-
-inline _LIBCPP_HIDE_FROM_ABI float strtof_l(const char* __nptr, char** __endptr, locale_t) {
-  return ::strtof(__nptr, __endptr);
-}
-
-inline _LIBCPP_HIDE_FROM_ABI double strtod_l(const char* __nptr, char** __endptr, locale_t) {
-  return ::strtod(__nptr, __endptr);
-}
-
-inline _LIBCPP_HIDE_FROM_ABI long double strtold_l(const char* __nptr, char** __endptr, locale_t) {
-  return ::strtold(__nptr, __endptr);
-}
-
-#endif // _LIBCPP___SUPPORT_XLOCALE_STRTONUM_FALLBACK_H
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index 5ae83332b6fa..5fa74b5b5db7 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -1613,13 +1613,13 @@ module std [system] {
       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/openbsd.h"
       textual header "__locale_dir/support/windows.h"
     }
 
     module locale_base_api {
       textual header "__locale_dir/locale_base_api/bsd_locale_fallbacks.h"
       textual header "__locale_dir/locale_base_api/ibm.h"
-      textual header "__locale_dir/locale_base_api/openbsd.h"
     }
     export *
   }