diff --git a/libcxx/test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp b/libcxx/test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp
--- a/libcxx/test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp
+++ b/libcxx/test/libcxx/language.support/support.dynamic/libcpp_deallocate.sh.cpp
@@ -13,13 +13,14 @@
 // definitions, which does not yet provide aligned allocation
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
-// The dylibs shipped before macosx10.13 do not contain the aligned allocation
-// functions, so trying to force using those with -faligned-allocation results
-// in a link error.
+// The dynamic library shipped with z/OS and Mac OS X before macosx10.13 do not
+// contain the aligned allocation functions, so trying to force using those
+// with -faligned-allocation results in a link error.
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.12
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.11
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.10
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.9
+// XFAIL: -zos
 
 // AppleClang < 10 incorrectly warns that aligned allocation is not supported
 // even when it is supported.
diff --git a/libcxx/test/libcxx/language.support/support.dynamic/new_faligned_allocation.pass.cpp b/libcxx/test/libcxx/language.support/support.dynamic/new_faligned_allocation.pass.cpp
--- a/libcxx/test/libcxx/language.support/support.dynamic/new_faligned_allocation.pass.cpp
+++ b/libcxx/test/libcxx/language.support/support.dynamic/new_faligned_allocation.pass.cpp
@@ -13,13 +13,14 @@
 // definitions, which does not yet provide aligned allocation
 // XFAIL: LIBCXX-WINDOWS-FIXME
 
-// The dylibs shipped before macosx10.13 do not contain the aligned allocation
-// functions, so trying to force using those with -faligned-allocation results
-// in a link error.
+// The dynamic library shipped with z/OS and Mac OS X before macosx10.13 do not
+// contain the aligned allocation functions, so trying to force using those
+// with -faligned-allocation results in a link error.
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.12
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.11
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.10
 // XFAIL: use_system_cxx_lib && x86_64-apple-macosx10.9
+// XFAIL: -zos
 
 // REQUIRES: -faligned-allocation
 // ADDITIONAL_COMPILE_FLAGS: -faligned-allocation