diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1219,8 +1219,9 @@
 #  endif
 #endif
 
-#if defined(__BIONIC__) || defined(__CloudABI__) ||                            \
-    defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC)
+#if defined(__BIONIC__) || defined(__CloudABI__) || \
+    defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC) || \
+    defined(__MVS__)
 #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
@@ -21,7 +21,7 @@
 #if defined(_LIBCPP_MSVCRT_LIKE)
 # include <cstring>
 # include <support/win32/locale_win32.h>
-#elif defined(_AIX)
+#elif defined(_AIX) || defined(__MVS__)
 # include <support/ibm/xlocale.h>
 #elif defined(__ANDROID__)
 # include <support/android/locale_bionic.h>
diff --git a/libcxx/include/support/ibm/xlocale.h b/libcxx/include/support/ibm/xlocale.h
--- a/libcxx/include/support/ibm/xlocale.h
+++ b/libcxx/include/support/ibm/xlocale.h
@@ -11,13 +11,13 @@
 #define _LIBCPP_SUPPORT_IBM_XLOCALE_H
 #include <support/ibm/locale_mgmt_aix.h>
 
-#if defined(_AIX)
 #include "cstdlib"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if defined(_AIX)
 #if !defined(_AIX71)
 // AIX 7.1 and higher has these definitions.  Definitions and stubs
 // are provied here as a temporary workaround on AIX 6.1.
@@ -207,14 +207,20 @@
 }
 #endif // !defined(_AIX71)
 
-// strftime_l() is defined by POSIX. However, AIX 7.1 does not have it
-// implemented yet.
+// strftime_l() is defined by POSIX. However, AIX 7.1 and z/OS do not have it
+// implemented yet. z/OS retrieves it from the POSIX fallbacks.
 static inline
 size_t strftime_l(char *__s, size_t __size, const char *__fmt,
                   const struct tm *__tm, locale_t locale) {
   return __xstrftime(locale, __s, __size, __fmt, __tm);
 }
 
+#elif defined(__MVS__)
+#include <wctype.h>
+// POSIX routines
+#include <support/xlocale/__posix_l_fallback.h>
+#endif // defined(__MVS__)
+
 // The following are not POSIX routines.  These are quick-and-dirty hacks
 // to make things pretend to work
 static inline
@@ -266,5 +272,4 @@
 #ifdef __cplusplus
 }
 #endif
-#endif // defined(_AIX)
 #endif // _LIBCPP_SUPPORT_IBM_XLOCALE_H