diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -285,6 +285,8 @@
 option(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY
     "Build libc++ with an externalized threading library.
      This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON" OFF)
+option(LIBCXXX_DISABLE_APPLE_ULOCK_WAIT
+    "Build libc++ without __ulock_wait on Apple platforms" OFF)
 
 # Misc options ----------------------------------------------------------------
 # FIXME: Turn -pedantic back ON. It is currently off because it warns
@@ -857,6 +859,9 @@
 else()
   config_define(0 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT)
 endif()
+if (APPLE)
+  config_define_if(LIBCXXX_DISABLE_APPLE_ULOCK_WAIT _LIBCXXX_DISABLE_ULOCK_WAIT)
+endif()
 
 if (LIBCXX_ABI_DEFINES)
   set(abi_defines)
diff --git a/libcxx/include/__config_site.in b/libcxx/include/__config_site.in
--- a/libcxx/include/__config_site.in
+++ b/libcxx/include/__config_site.in
@@ -32,6 +32,9 @@
 #cmakedefine _LIBCPP_HAS_NO_WIDE_CHARACTERS
 #cmakedefine01 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT
 #cmakedefine _LIBCPP_ENABLE_DEBUG_MODE
+#ifdef __APPLE__
+#cmakedefine _LIBCXXX_DISABLE_ULOCK_WAIT
+#endif
 
 // __USE_MINGW_ANSI_STDIO gets redefined on MinGW
 #ifdef __clang__
diff --git a/libcxx/src/atomic.cpp b/libcxx/src/atomic.cpp
--- a/libcxx/src/atomic.cpp
+++ b/libcxx/src/atomic.cpp
@@ -26,6 +26,9 @@
 # define SYS_futex SYS_futex_time64
 #endif
 
+#elif defined(__APPLE__)
+#include "include/apple_availability.h"
+
 #elif defined(__FreeBSD__)
 
 #include <sys/types.h>
diff --git a/libcxx/src/include/apple_availability.h b/libcxx/src/include/apple_availability.h
--- a/libcxx/src/include/apple_availability.h
+++ b/libcxx/src/include/apple_availability.h
@@ -29,6 +29,7 @@
 #endif
 #endif // __ENVIRONMENT_.*_VERSION_MIN_REQUIRED__
 
+#if !defined(_LIBCXXX_DISABLE_ULOCK_WAIT)
 #if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
 #if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101500
 #define _LIBCPP_USE_ULOCK
@@ -46,6 +47,7 @@
 #define _LIBCPP_USE_ULOCK
 #endif
 #endif // __ENVIRONMENT_.*_VERSION_MIN_REQUIRED__
+#endif // _LIBCXXX_DISABLE_ULOCK_WAIT
 
 #endif // __APPLE__