diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -159,6 +159,7 @@
   support/musl/xlocale.h
   support/newlib/xlocale.h
   support/nuttx/xlocale.h
+  support/openbsd/xlocale.h
   support/solaris/floatingpoint.h
   support/solaris/wchar.h
   support/solaris/xlocale.h
diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -264,14 +264,14 @@
 #  endif  // __LONG_LONG_SUPPORTED
 #endif  // __FreeBSD__
 
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__OpenBSD__)
 #  include <sys/endian.h>
 #  if _BYTE_ORDER == _LITTLE_ENDIAN
 #    define _LIBCPP_LITTLE_ENDIAN
 #  else  // _BYTE_ORDER == _LITTLE_ENDIAN
 #    define _LIBCPP_BIG_ENDIAN
 #  endif  // _BYTE_ORDER == _LITTLE_ENDIAN
-#endif  // __NetBSD__
+#endif  // defined(__NetBSD__) || defined(__OpenBSD__)
 
 #if defined(_WIN32)
 #  define _LIBCPP_WIN32API
@@ -312,7 +312,7 @@
 #  endif
 #endif // __sun__
 
-#if defined(__CloudABI__)
+#if defined(__OpenBSD__) || defined(__CloudABI__)
    // Certain architectures provide arc4random(). Prefer using
    // arc4random() over /dev/{u,}random to make it possible to obtain
    // random data even when using sandboxing mechanisms such as chroots,
@@ -370,6 +370,9 @@
 #    define _LIBCPP_HAS_ALIGNED_ALLOC
 #    define _LIBCPP_HAS_QUICK_EXIT
 #    define _LIBCPP_HAS_TIMESPEC_GET
+#  elif defined(__OpenBSD__)
+#    define _LIBCPP_HAS_ALIGNED_ALLOC
+#    define _LIBCPP_HAS_TIMESPEC_GET
 #  elif defined(__linux__)
 #    if !defined(_LIBCPP_HAS_MUSL_LIBC)
 #      if _LIBCPP_GLIBC_PREREQ(2, 15) || defined(__BIONIC__)
@@ -1109,6 +1112,7 @@
 #  if defined(__FreeBSD__) || \
       defined(__wasi__) || \
       defined(__NetBSD__) || \
+      defined(__OpenBSD__) || \
       defined(__NuttX__) || \
       defined(__linux__) || \
       defined(__GNU__) || \
@@ -1204,14 +1208,15 @@
 // Some systems do not provide gets() in their C library, for security reasons.
 #ifndef _LIBCPP_C_HAS_NO_GETS
 #  if defined(_LIBCPP_MSVCRT) || \
-      (defined(__FreeBSD_version) && __FreeBSD_version >= 1300043)
+      (defined(__FreeBSD_version) && __FreeBSD_version >= 1300043) || \
+      defined(__OpenBSD__)
 #    define _LIBCPP_C_HAS_NO_GETS
 #  endif
 #endif
 
 #if defined(__BIONIC__) || defined(__CloudABI__) || defined(__NuttX__) ||      \
     defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC) || \
-    defined(__MVS__)
+    defined(__MVS__) || defined(__OpenBSD__)
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 #endif
 
diff --git a/libcxx/include/__locale b/libcxx/include/__locale
--- a/libcxx/include/__locale
+++ b/libcxx/include/__locale
@@ -33,6 +33,8 @@
 # include <support/solaris/xlocale.h>
 #elif defined(_NEWLIB_VERSION)
 # include <support/newlib/xlocale.h>
+#elif defined(__OpenBSD__)
+# include <support/openbsd/xlocale.h>
 #elif (defined(__APPLE__)      || defined(__FreeBSD__) \
     || defined(__EMSCRIPTEN__) || defined(__IBMCPP__))
 # include <xlocale.h>
diff --git a/libcxx/include/support/openbsd/xlocale.h b/libcxx/include/support/openbsd/xlocale.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/support/openbsd/xlocale.h
@@ -0,0 +1,19 @@
+// -*- C++ -*-
+//===-------------------- support/openbsd/xlocale.h -----------------------===//
+//
+// 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_SUPPORT_OPENBSD_XLOCALE_H
+#define _LIBCPP_SUPPORT_OPENBSD_XLOCALE_H
+
+#include <cstdlib>
+#include <clocale>
+#include <cwctype>
+#include <ctype.h>
+#include <support/xlocale/__strtonum_fallback.h>
+
+#endif