diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -240,6 +240,8 @@
 option(LIBCXX_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
 option(LIBCXX_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXX_DISABLE_MACRO_CONFLICT_WARNINGS "Disable #warnings about conflicting macros." OFF)
+option(LIBCXX_TEST_HAVE_FORK "Target system has fork()/wait() support available for test suite." ON)
+config_define_if(LIBCXX_TEST_HAVE_FORK _LIBCPP_TEST_HAVE_FORK)
 
 option(LIBCXX_GENERATE_COVERAGE "Enable generating code coverage." OFF)
 set(LIBCXX_COVERAGE_LIBRARY "" CACHE STRING
diff --git a/libcxx/test/CMakeLists.txt b/libcxx/test/CMakeLists.txt
--- a/libcxx/test/CMakeLists.txt
+++ b/libcxx/test/CMakeLists.txt
@@ -40,6 +40,7 @@
 pythonize_bool(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
 pythonize_bool(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
 pythonize_bool(LIBCXX_DEBUG_BUILD)
+pythonize_bool(LIBCXX_TEST_HAVE_FORK)
 
 # By default, for non-standalone builds, libcxx and libcxxabi share a library
 # directory.
diff --git a/libcxx/test/libcxx/containers/sequences/array/array.zero/db_back.pass.cpp b/libcxx/test/libcxx/containers/sequences/array/array.zero/db_back.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/array/array.zero/db_back.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/array/array.zero/db_back.pass.cpp
@@ -10,7 +10,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test array<T, 0>::front() raises a debug error.
diff --git a/libcxx/test/libcxx/containers/sequences/array/array.zero/db_front.pass.cpp b/libcxx/test/libcxx/containers/sequences/array/array.zero/db_front.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/array/array.zero/db_front.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/array/array.zero/db_front.pass.cpp
@@ -10,7 +10,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test array<T, 0>::front() raises a debug error.
diff --git a/libcxx/test/libcxx/containers/sequences/array/array.zero/db_indexing.pass.cpp b/libcxx/test/libcxx/containers/sequences/array/array.zero/db_indexing.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/array/array.zero/db_indexing.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/array/array.zero/db_indexing.pass.cpp
@@ -10,7 +10,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test array<T, 0>::operator[] raises a debug error.
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.cons/db_copy.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.cons/db_copy.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.cons/db_copy.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.cons/db_copy.pass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // <list>
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // list(list&& c);
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.cons/db_move.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.cons/db_move.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.cons/db_move.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.cons/db_move.pass.cpp
@@ -8,7 +8,7 @@
 
 // UNSUPPORTED: c++98, c++03
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/emplace_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/emplace_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/emplace_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/emplace_db1.pass.cpp
@@ -8,7 +8,7 @@
 
 // UNSUPPORTED: c++98, c++03
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db2.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db2.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db2.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db2.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db2.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db2.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db2.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db2.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db3.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db3.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db3.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db3.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db4.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db4.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db4.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db4.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_iter_iter_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_iter_iter_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_iter_iter_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_iter_iter_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_rvalue_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_rvalue_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_rvalue_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_rvalue_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_size_value_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_size_value_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_size_value_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_size_value_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_value_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_value_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_value_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_value_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/pop_back_db1.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/pop_back_db1.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.modifiers/pop_back_db1.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.modifiers/pop_back_db1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter_iter.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter_iter.pass.cpp
--- a/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter_iter.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter_iter.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
diff --git a/libcxx/test/libcxx/debug/containers/db_associative_container_tests.pass.cpp b/libcxx/test/libcxx/debug/containers/db_associative_container_tests.pass.cpp
--- a/libcxx/test/libcxx/debug/containers/db_associative_container_tests.pass.cpp
+++ b/libcxx/test/libcxx/debug/containers/db_associative_container_tests.pass.cpp
@@ -11,7 +11,7 @@
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
diff --git a/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.multithread.pass.cpp b/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.multithread.pass.cpp
--- a/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.multithread.pass.cpp
+++ b/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.multithread.pass.cpp
@@ -11,7 +11,7 @@
 // UNSUPPORTED: libcpp-has-no-threads
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test multihtreaded container debugging
diff --git a/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.pass.cpp b/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.pass.cpp
--- a/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.pass.cpp
+++ b/libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.pass.cpp
@@ -11,7 +11,7 @@
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
diff --git a/libcxx/test/libcxx/debug/containers/db_string.pass.cpp b/libcxx/test/libcxx/debug/containers/db_string.pass.cpp
--- a/libcxx/test/libcxx/debug/containers/db_string.pass.cpp
+++ b/libcxx/test/libcxx/debug/containers/db_string.pass.cpp
@@ -11,7 +11,7 @@
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
diff --git a/libcxx/test/libcxx/debug/containers/db_unord_container_tests.pass.cpp b/libcxx/test/libcxx/debug/containers/db_unord_container_tests.pass.cpp
--- a/libcxx/test/libcxx/debug/containers/db_unord_container_tests.pass.cpp
+++ b/libcxx/test/libcxx/debug/containers/db_unord_container_tests.pass.cpp
@@ -11,7 +11,7 @@
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
diff --git a/libcxx/test/libcxx/debug/debug_abort.pass.cpp b/libcxx/test/libcxx/debug/debug_abort.pass.cpp
--- a/libcxx/test/libcxx/debug/debug_abort.pass.cpp
+++ b/libcxx/test/libcxx/debug/debug_abort.pass.cpp
@@ -9,7 +9,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // Test that the default debug handler aborts the program.
diff --git a/libcxx/test/libcxx/debug/debug_helper_test.pass.cpp b/libcxx/test/libcxx/debug/debug_helper_test.pass.cpp
--- a/libcxx/test/libcxx/debug/debug_helper_test.pass.cpp
+++ b/libcxx/test/libcxx/debug/debug_helper_test.pass.cpp
@@ -10,7 +10,7 @@
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
diff --git a/libcxx/test/libcxx/debug/debug_register.pass.cpp b/libcxx/test/libcxx/debug/debug_register.pass.cpp
--- a/libcxx/test/libcxx/debug/debug_register.pass.cpp
+++ b/libcxx/test/libcxx/debug/debug_register.pass.cpp
@@ -9,7 +9,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 #define _LIBCPP_DEBUG 1
diff --git a/libcxx/test/libcxx/input.output/filesystems/class.path/path.itr/iterator_db.pass.cpp b/libcxx/test/libcxx/input.output/filesystems/class.path/path.itr/iterator_db.pass.cpp
--- a/libcxx/test/libcxx/input.output/filesystems/class.path/path.itr/iterator_db.pass.cpp
+++ b/libcxx/test/libcxx/input.output/filesystems/class.path/path.itr/iterator_db.pass.cpp
@@ -9,6 +9,7 @@
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
 // <filesystem>
diff --git a/libcxx/test/libcxx/iterators/advance.debug1.pass.cpp b/libcxx/test/libcxx/iterators/advance.debug1.pass.cpp
--- a/libcxx/test/libcxx/iterators/advance.debug1.pass.cpp
+++ b/libcxx/test/libcxx/iterators/advance.debug1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
diff --git a/libcxx/test/libcxx/iterators/next.debug1.pass.cpp b/libcxx/test/libcxx/iterators/next.debug1.pass.cpp
--- a/libcxx/test/libcxx/iterators/next.debug1.pass.cpp
+++ b/libcxx/test/libcxx/iterators/next.debug1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
diff --git a/libcxx/test/libcxx/iterators/prev.debug1.pass.cpp b/libcxx/test/libcxx/iterators/prev.debug1.pass.cpp
--- a/libcxx/test/libcxx/iterators/prev.debug1.pass.cpp
+++ b/libcxx/test/libcxx/iterators/prev.debug1.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 // UNSUPPORTED: with_system_cxx_lib
 // UNSUPPORTED: c++98, c++03
diff --git a/libcxx/test/libcxx/thread/futures/futures.promise/set_exception.pass.cpp b/libcxx/test/libcxx/thread/futures/futures.promise/set_exception.pass.cpp
--- a/libcxx/test/libcxx/thread/futures/futures.promise/set_exception.pass.cpp
+++ b/libcxx/test/libcxx/thread/futures/futures.promise/set_exception.pass.cpp
@@ -12,7 +12,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <future>
diff --git a/libcxx/test/libcxx/thread/futures/futures.promise/set_exception_at_thread_exit.pass.cpp b/libcxx/test/libcxx/thread/futures/futures.promise/set_exception_at_thread_exit.pass.cpp
--- a/libcxx/test/libcxx/thread/futures/futures.promise/set_exception_at_thread_exit.pass.cpp
+++ b/libcxx/test/libcxx/thread/futures/futures.promise/set_exception_at_thread_exit.pass.cpp
@@ -12,7 +12,7 @@
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <future>
diff --git a/libcxx/test/lit.site.cfg.in b/libcxx/test/lit.site.cfg.in
--- a/libcxx/test/lit.site.cfg.in
+++ b/libcxx/test/lit.site.cfg.in
@@ -24,6 +24,7 @@
 config.target_info              = "@LIBCXX_TARGET_INFO@"
 config.test_linker_flags        = "@LIBCXX_TEST_LINKER_FLAGS@"
 config.test_compiler_flags      = "@LIBCXX_TEST_COMPILER_FLAGS@"
+config.test_has_fork            = "@LIBCXX_TEST_HAVE_FORK@"
 
 config.executor                 = "@LIBCXX_EXECUTOR@"
 config.llvm_unwinder            = @LIBCXXABI_USE_LLVM_UNWINDER@
diff --git a/libcxx/test/support/debug_mode_helper.h b/libcxx/test/support/debug_mode_helper.h
--- a/libcxx/test/support/debug_mode_helper.h
+++ b/libcxx/test/support/debug_mode_helper.h
@@ -18,6 +18,10 @@
 #error "This header may only be used for libc++ tests"
 #endif
 
+#ifndef _LIBCPP_TEST_HAVE_FORK
+#error "This header may only be used on systems that support fork() and wait()"
+#endif
+
 #include <__debug>
 #include <utility>
 #include <cstddef>
diff --git a/libcxx/utils/libcxx/test/config.py b/libcxx/utils/libcxx/test/config.py
--- a/libcxx/utils/libcxx/test/config.py
+++ b/libcxx/utils/libcxx/test/config.py
@@ -879,6 +879,8 @@
         if debug_level not in ['0', '1']:
             self.lit_config.fatal('Invalid value for debug_level "%s".'
                                   % debug_level)
+        if self.config.test_has_fork:
+            self.config.available_features.add('has-fork')
         self.cxx.compile_flags += ['-D_LIBCPP_DEBUG=%s' % debug_level]
 
     def configure_warnings(self):