Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -71,6 +71,7 @@
 option(LIBCXX_ENABLE_FILESYSTEM "Build filesystem as part of libc++experimental.a"
     ${ENABLE_FILESYSTEM_DEFAULT})
 option(LIBCXX_INCLUDE_TESTS "Build the libc++ tests." ${LLVM_INCLUDE_TESTS})
+option(LIBCXX_ENABLE_RANDOM_DEVICE "Build random_device class" ON)
 
 # Benchmark options -----------------------------------------------------------
 option(LIBCXX_INCLUDE_BENCHMARKS "Build the libc++ benchmarks and their dependancies" ON)
@@ -629,6 +630,7 @@
 config_define_if_not(LIBCXX_ENABLE_THREADS _LIBCPP_HAS_NO_THREADS)
 config_define_if_not(LIBCXX_ENABLE_MONOTONIC_CLOCK _LIBCPP_HAS_NO_MONOTONIC_CLOCK)
 config_define_if_not(LIBCXX_ENABLE_THREAD_UNSAFE_C_FUNCTIONS _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS)
+config_define_if_not(LIBCXX_ENABLE_RANDOM_DEVICE _LIBCPP_HAS_NO_RANDOM_DEVICE)
 
 config_define_if(LIBCXX_HAS_PTHREAD_API _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define_if(LIBCXX_HAS_EXTERNAL_THREAD_API _LIBCPP_HAS_THREAD_API_EXTERNAL)
Index: include/__config_site.in
===================================================================
--- include/__config_site.in
+++ include/__config_site.in
@@ -20,6 +20,7 @@
 #cmakedefine _LIBCPP_HAS_NO_THREADS
 #cmakedefine _LIBCPP_HAS_NO_MONOTONIC_CLOCK
 #cmakedefine _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
+#cmakedefine _LIBCPP_HAS_NO_RANDOM_DEVICE
 #cmakedefine _LIBCPP_HAS_MUSL_LIBC
 #cmakedefine _LIBCPP_HAS_THREAD_API_PTHREAD
 #cmakedefine _LIBCPP_HAS_THREAD_API_EXTERNAL
Index: include/random
===================================================================
--- include/random
+++ include/random
@@ -3476,6 +3476,7 @@
 
 typedef shuffle_order_engine<minstd_rand0, 256>                         knuth_b;
 
+#ifndef _LIBCPP_HAS_NO_RANDOM_DEVICE
 // random_device
 
 class _LIBCPP_TYPE_VIS random_device
@@ -3511,6 +3512,7 @@
     random_device(const random_device&); // = delete;
     random_device& operator=(const random_device&); // = delete;
 };
+#endif // _LIBCPP_HAS_NO_RANDOM_DEVICE
 
 // seed_seq
 
Index: src/random.cpp
===================================================================
--- src/random.cpp
+++ src/random.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include <__config>
+#ifndef _LIBCPP_HAS_NO_RANDOM_DEVICE
 
 #if defined(_LIBCPP_USING_WIN32_RANDOM)
 // Must be defined before including stdlib.h to enable rand_s().
@@ -177,3 +178,4 @@
 }
 
 _LIBCPP_END_NAMESPACE_STD
+#endif // _LIBCPP_HAS_NO_RANDOM_DEVICE
Index: test/std/numerics/rand/rand.device/lit.local.cfg
===================================================================
--- /dev/null
+++ test/std/numerics/rand/rand.device/lit.local.cfg
@@ -0,0 +1,3 @@
+# Disable all of the random device tests if the correct feature is not available.
+if 'libcpp-has-no-random-device' in config.available_features:
+  config.unsupported = True
Index: test/support/filesystem_test_helper.hpp
===================================================================
--- test/support/filesystem_test_helper.hpp
+++ test/support/filesystem_test_helper.hpp
@@ -107,7 +107,10 @@
 struct scoped_test_env
 {
     scoped_test_env() : test_root(random_env_path())
-        { fs_helper_run(fs_make_cmd("init_test_directory", test_root)); }
+        { fs_helper_run(fs_make_cmd("init_test_directory", test_root));
+          auto now = std::chrono::high_resolution_clock::now();
+          srand(now.time_since_epoch().count());
+        }
 
     ~scoped_test_env()
         { fs_helper_run(fs_make_cmd("destroy_test_directory", test_root)); }
@@ -184,9 +187,7 @@
     }
 
     static char random_hex_char() {
-        static std::mt19937 rd { std::random_device{}() };
-        static std::uniform_int_distribution<int> mrand{0, 15};
-        return to_hex( mrand(rd) );
+        return to_hex(rand() & 0xF);
     }
 
     static std::string unique_path_suffix() {