diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -521,6 +521,20 @@
           limit: 2
     timeout_in_minutes: 120
 
+  # TODO: When this is ready, this should become the default and we can remove this job.
+  - label: "With PSTL support"
+    command: "libcxx/utils/ci/run-buildbot with-pstl"
+    artifact_paths:
+      - "**/test-results.xml"
+    agents:
+      queue: "libcxx-builders"
+      os: "linux"
+    retry:
+      automatic:
+        - exit_status: -1  # Agent was lost
+          limit: 2
+    timeout_in_minutes: 120
+
   # Other non-testing CI jobs
   - label: "Benchmarks"
     command: "libcxx/utils/ci/run-buildbot benchmarks"
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -90,7 +90,7 @@
 
 function generate-cmake() {
     generate-cmake-base \
-          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
+          -DLLVM_ENABLE_RUNTIMES="pstl;libcxx;libcxxabi;libunwind" \
           -DLIBCXX_CXX_ABI=libcxxabi \
           "${@}"
 }
@@ -398,6 +398,17 @@
                    -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in"
     check-runtimes
 ;;
+with-pstl)
+    export CC=clang
+    export CXX=clang++
+    clean
+    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx20.cmake" \
+                   -DLIBCXX_TEST_CONFIG="llvm-libc++-shared.cfg.in" \
+                   -DLIBUNWIND_TEST_CONFIG="llvm-libunwind-shared.cfg.in" \
+                   -DCMAKE_BUILD_WITH_INSTALL_RPATH=TRUE \
+                   -DLIBCXX_ENABLE_PARALLEL_ALGORITHMS=ON
+    check-runtimes
+;;
 generic-no-experimental)
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-no-experimental.cmake" \
diff --git a/pstl/include/pstl/internal/algorithm_impl.h b/pstl/include/pstl/internal/algorithm_impl.h
--- a/pstl/include/pstl/internal/algorithm_impl.h
+++ b/pstl/include/pstl/internal/algorithm_impl.h
@@ -26,6 +26,9 @@
 
 _PSTL_HIDE_FROM_ABI_PUSH
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 namespace __pstl
 {
 namespace __internal
@@ -3814,6 +3817,8 @@
 } // namespace __internal
 } // namespace __pstl
 
+_LIBCPP_POP_MACROS
+
 _PSTL_HIDE_FROM_ABI_POP
 
 #endif /* _PSTL_ALGORITHM_IMPL_H */
diff --git a/pstl/include/pstl/internal/execution_defs.h b/pstl/include/pstl/internal/execution_defs.h
--- a/pstl/include/pstl/internal/execution_defs.h
+++ b/pstl/include/pstl/internal/execution_defs.h
@@ -49,7 +49,7 @@
 constexpr unsequenced_policy unseq{};
 
 // 2.3, Execution policy type trait
-template <class T>
+template <class _Tp>
 struct is_execution_policy : std::false_type
 {
 };
@@ -72,8 +72,8 @@
 };
 
 #if defined(_PSTL_CPP14_VARIABLE_TEMPLATES_PRESENT)
-template <class T>
-constexpr bool is_execution_policy_v = __pstl::execution::is_execution_policy<T>::value;
+template <class _Tp>
+constexpr bool is_execution_policy_v = __pstl::execution::is_execution_policy<_Tp>::value;
 #endif
 
 } // namespace v1
@@ -81,10 +81,10 @@
 
 namespace __internal
 {
-template <class ExecPolicy, class T>
+template <class _ExecPolicy, class _Tp>
 using __enable_if_execution_policy =
-    typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<ExecPolicy>::type>::value,
-                            T>::type;
+    typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<_ExecPolicy>::type>::value,
+                            _Tp>::type;
 
 template <class _IsVector>
 struct __serial_tag;
diff --git a/pstl/include/pstl/internal/pstl_config.h b/pstl/include/pstl/internal/pstl_config.h
--- a/pstl/include/pstl/internal/pstl_config.h
+++ b/pstl/include/pstl/internal/pstl_config.h
@@ -28,8 +28,8 @@
 #endif
 
 #if !defined(_PSTL_ASSERT)
-#    include <cassert>
-#    define _PSTL_ASSERT(pred) (assert((pred)))
+#    include <__assert>
+#    define _PSTL_ASSERT(pred) (_LIBCPP_ASSERT((pred), ""))
 #endif
 
 // Portability "#pragma" definition