diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -521,8 +521,12 @@
 
   # When building the dylib, don't warn for unavailable aligned allocation
   # functions based on the deployment target -- they are always available
-  # because they are provided by the dylib itself.
-  target_add_compile_flags_if_supported(${target} PRIVATE -faligned-allocation)
+  # because they are provided by the dylib itself with the excepton of z/OS.
+  if (ZOS)
+    target_add_compile_flags_if_supported(${target} PRIVATE -fno-aligned-allocation)
+  else()
+    target_add_compile_flags_if_supported(${target} PRIVATE -faligned-allocation)
+  endif()
 
   # On all systems the system c++ standard library headers need to be excluded.
   # MSVC only has -X, which disables all default includes; including the crt.
diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -943,6 +943,8 @@
    // We're deferring to Microsoft's STL to provide aligned new et al. We don't
    // have it unless the language feature test macro is defined.
 #  define _LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
+#elif defined(__MVS__)
+#  define _LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
 #endif
 
 #if defined(__APPLE__)