diff --git a/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp b/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp
--- a/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp
+++ b/libcxx/test/libcxx/input.output/filesystems/class.directory_entry/directory_entry.mods/last_write_time.pass.cpp
@@ -15,6 +15,9 @@
 // other platforms.
 // UNSUPPORTED: windows
 
+// This test assumes that time is stored as a 64 bit value when on MVS it is stored as 32 bit
+// UNSUPPORTED: target={{.+}}-zos{{.*}}
+
 // TODO(ldionne): This test fails on Ubuntu Focal on our CI nodes (and only there), in 32 bit mode.
 // UNSUPPORTED: linux && 32bits-on-64bits
 
diff --git a/libcxx/test/support/filesystem_test_helper.h b/libcxx/test/support/filesystem_test_helper.h
--- a/libcxx/test/support/filesystem_test_helper.h
+++ b/libcxx/test/support/filesystem_test_helper.h
@@ -193,10 +193,10 @@
             abort();
         }
 
-#ifndef _WIN32
-#define FOPEN_CLOEXEC_FLAG "e"
+#if defined(_WIN32) || defined(__MVS__)
+#  define FOPEN_CLOEXEC_FLAG ""
 #else
-#define FOPEN_CLOEXEC_FLAG ""
+#  define FOPEN_CLOEXEC_FLAG "e"
 #endif
         FILE* file = large_file_fopen(filename.c_str(), "w" FOPEN_CLOEXEC_FLAG);
         if (file == nullptr) {