diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -102,6 +102,7 @@
   __charconv/chars_format.h
   __charconv/from_chars_result.h
   __charconv/to_chars_result.h
+  __chrono/convert_to_timespec.h
   __compare/common_comparison_category.h
   __compare/compare_three_way.h
   __compare/compare_three_way_result.h
@@ -356,6 +357,7 @@
   __support/xlocale/__posix_l_fallback.h
   __support/xlocale/__strtonum_fallback.h
   __thread/poll_with_backoff.h
+  __thread/timed_backoff_policy.h
   __threading_support
   __tree
   __tuple
diff --git a/libcxx/include/__chrono/convert_to_timespec.h b/libcxx/include/__chrono/convert_to_timespec.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__chrono/convert_to_timespec.h
@@ -0,0 +1,54 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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___CHRONO_CONVERT_TO_TIMESPEC_H
+#define _LIBCPP___CHRONO_CONVERT_TO_TIMESPEC_H
+
+#include <__config>
+#include <chrono>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// Convert a nanoseconds duration to the given TimeSpec type, which must have
+// the same properties as std::timespec.
+template <class _TimeSpec>
+_LIBCPP_HIDE_FROM_ABI inline
+_TimeSpec __convert_to_timespec(const chrono::nanoseconds& __ns)
+{
+  using namespace chrono;
+  seconds __s = duration_cast<seconds>(__ns);
+  _TimeSpec __ts;
+  typedef decltype(__ts.tv_sec) __ts_sec;
+  const __ts_sec __ts_sec_max = numeric_limits<__ts_sec>::max();
+
+  if (__s.count() < __ts_sec_max)
+  {
+    __ts.tv_sec = static_cast<__ts_sec>(__s.count());
+    __ts.tv_nsec = static_cast<decltype(__ts.tv_nsec)>((__ns - __s).count());
+  }
+  else
+  {
+    __ts.tv_sec = __ts_sec_max;
+    __ts.tv_nsec = 999999999; // (10^9 - 1)
+  }
+
+  return __ts;
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___CHRONO_CONVERT_TO_TIMESPEC_H
diff --git a/libcxx/include/__thread/timed_backoff_policy.h b/libcxx/include/__thread/timed_backoff_policy.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__thread/timed_backoff_policy.h
@@ -0,0 +1,45 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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___THREAD_TIMED_BACKOFF_POLICY_H
+#define _LIBCPP___THREAD_TIMED_BACKOFF_POLICY_H
+
+#include <__config>
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+
+#include <__threading_support>
+#include <chrono>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+struct __libcpp_timed_backoff_policy {
+  _LIBCPP_INLINE_VISIBILITY
+  bool operator()(chrono::nanoseconds __elapsed) const
+  {
+      if(__elapsed > chrono::milliseconds(128))
+          __libcpp_thread_sleep_for(chrono::milliseconds(8));
+      else if(__elapsed > chrono::microseconds(64))
+          __libcpp_thread_sleep_for(__elapsed / 2);
+      else if(__elapsed > chrono::microseconds(4))
+        __libcpp_thread_yield();
+      else
+        {} // poll
+      return false;
+  }
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_NO_THREADS
+
+#endif // _LIBCPP___THREAD_TIMED_BACKOFF_POLICY_H
diff --git a/libcxx/include/__threading_support b/libcxx/include/__threading_support
--- a/libcxx/include/__threading_support
+++ b/libcxx/include/__threading_support
@@ -54,9 +54,6 @@
 typedef ::timespec __libcpp_timespec_t;
 #endif // !defined(_LIBCPP_HAS_NO_THREADS)
 
-_LIBCPP_PUSH_MACROS
-#include <__undef_macros>
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if !defined(_LIBCPP_HAS_NO_THREADS)
@@ -252,53 +249,9 @@
 
 #endif // !defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
 
-struct __libcpp_timed_backoff_policy {
-  _LIBCPP_INLINE_VISIBILITY
-  bool operator()(chrono::nanoseconds __elapsed) const
-  {
-      if(__elapsed > chrono::milliseconds(128))
-          __libcpp_thread_sleep_for(chrono::milliseconds(8));
-      else if(__elapsed > chrono::microseconds(64))
-          __libcpp_thread_sleep_for(__elapsed / 2);
-      else if(__elapsed > chrono::microseconds(4))
-        __libcpp_thread_yield();
-      else
-        {} // poll
-      return false;
-  }
-};
-
 #if (!defined(_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL) || \
      defined(_LIBCPP_BUILDING_THREAD_LIBRARY_EXTERNAL))
 
-
-namespace __thread_detail {
-
-_LIBCPP_HIDE_FROM_ABI inline
-__libcpp_timespec_t __convert_to_timespec(const chrono::nanoseconds& __ns)
-{
-  using namespace chrono;
-  seconds __s = duration_cast<seconds>(__ns);
-  __libcpp_timespec_t __ts;
-  typedef decltype(__ts.tv_sec) __ts_sec;
-  const __ts_sec __ts_sec_max = numeric_limits<__ts_sec>::max();
-
-  if (__s.count() < __ts_sec_max)
-  {
-    __ts.tv_sec = static_cast<__ts_sec>(__s.count());
-    __ts.tv_nsec = static_cast<decltype(__ts.tv_nsec)>((__ns - __s).count());
-  }
-  else
-  {
-    __ts.tv_sec = __ts_sec_max;
-    __ts.tv_nsec = 999999999; // (10^9 - 1)
-  }
-
-  return __ts;
-}
-
-} // namespace __thread_detail
-
 #if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 
 _LIBCPP_HIDE_FROM_ABI inline
@@ -479,7 +432,7 @@
 _LIBCPP_HIDE_FROM_ABI inline
 void __libcpp_thread_sleep_for(const chrono::nanoseconds& __ns)
 {
-   __libcpp_timespec_t __ts = __thread_detail::__convert_to_timespec(__ns);
+   __libcpp_timespec_t __ts = _VSTD::__convert_to_timespec<__libcpp_timespec_t>(__ns);
    while (nanosleep(&__ts, &__ts) == -1 && errno == EINTR);
 }
 
@@ -664,7 +617,7 @@
 _LIBCPP_HIDE_FROM_ABI inline
 void __libcpp_thread_sleep_for(const chrono::nanoseconds& __ns)
 {
-   __libcpp_timespec_t __ts = __thread_detail::__convert_to_timespec(__ns);
+   __libcpp_timespec_t __ts = _VSTD::__convert_to_timespec<__libcpp_timespec_t>(__ns);
   thrd_sleep(&__ts, nullptr);
 }
 
@@ -776,6 +729,4 @@
 
 _LIBCPP_END_NAMESPACE_STD
 
-_LIBCPP_POP_MACROS
-
 #endif // _LIBCPP_THREADING_SUPPORT
diff --git a/libcxx/include/atomic b/libcxx/include/atomic
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -521,6 +521,7 @@
 #include <__availability>
 #include <__config>
 #include <__thread/poll_with_backoff.h>
+#include <__thread/timed_backoff_policy.h>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
diff --git a/libcxx/include/barrier b/libcxx/include/barrier
--- a/libcxx/include/barrier
+++ b/libcxx/include/barrier
@@ -47,6 +47,7 @@
 
 #include <__availability>
 #include <__config>
+#include <__thread/timed_backoff_policy.h>
 #include <atomic>
 #ifndef _LIBCPP_HAS_NO_TREE_BARRIER
 # include <memory>
diff --git a/libcxx/include/chrono b/libcxx/include/chrono
--- a/libcxx/include/chrono
+++ b/libcxx/include/chrono
@@ -2835,4 +2835,7 @@
 
 _LIBCPP_POP_MACROS
 
+// TODO: Modularize <chrono> so this header doesn't have to sit alone here.
+#include <__chrono/convert_to_timespec.h>
+
 #endif // _LIBCPP_CHRONO
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -362,6 +362,10 @@
   module chrono {
     header "chrono"
     export *
+
+    module __chrono {
+      module convert_to_timespec { private header "__thread/convert_to_timespec.h" }
+    }
   }
   module codecvt {
     header "codecvt"
@@ -885,7 +889,8 @@
     export *
 
     module __thread {
-      module poll_with_backoff { private header "__thread/poll_with_backoff.h" }
+      module poll_with_backoff    { private header "__thread/poll_with_backoff.h" }
+      module timed_backoff_policy { private header "__thread/timed_backoff_policy.h" }
     }
   }
   module tuple {
diff --git a/libcxx/include/semaphore b/libcxx/include/semaphore
--- a/libcxx/include/semaphore
+++ b/libcxx/include/semaphore
@@ -47,6 +47,7 @@
 
 #include <__availability>
 #include <__config>
+#include <__thread/timed_backoff_policy.h>
 #include <__threading_support>
 #include <atomic>
 #include <version>
diff --git a/libcxx/include/thread b/libcxx/include/thread
--- a/libcxx/include/thread
+++ b/libcxx/include/thread
@@ -87,6 +87,7 @@
 #include <__functional_base>
 #include <__mutex_base>
 #include <__thread/poll_with_backoff.h>
+#include <__thread/timed_backoff_policy.h>
 #include <__threading_support>
 #include <__utility/forward.h>
 #include <chrono>
diff --git a/libcxx/src/atomic.cpp b/libcxx/src/atomic.cpp
--- a/libcxx/src/atomic.cpp
+++ b/libcxx/src/atomic.cpp
@@ -9,9 +9,10 @@
 #include <__config>
 #ifndef _LIBCPP_HAS_NO_THREADS
 
-#include <climits>
 #include <atomic>
+#include <climits>
 #include <functional>
+#include <thread>
 
 #ifdef __linux__
 
diff --git a/libcxx/test/libcxx/diagnostics/detail.headers/chrono/convert_to_timespec.module.verify.cpp b/libcxx/test/libcxx/diagnostics/detail.headers/chrono/convert_to_timespec.module.verify.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/detail.headers/chrono/convert_to_timespec.module.verify.cpp
@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__chrono/convert_to_timespec.h'}}
+#include <__chrono/convert_to_timespec.h>
diff --git a/libcxx/test/libcxx/diagnostics/detail.headers/thread/timed_backoff_policy.module.verify.cpp b/libcxx/test/libcxx/diagnostics/detail.headers/thread/timed_backoff_policy.module.verify.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/detail.headers/thread/timed_backoff_policy.module.verify.cpp
@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__thread/timed_backoff_policy.h'}}
+#include <__thread/timed_backoff_policy.h>