diff --git a/libcxx/cmake/caches/MinGW.cmake b/libcxx/cmake/caches/MinGW.cmake
--- a/libcxx/cmake/caches/MinGW.cmake
+++ b/libcxx/cmake/caches/MinGW.cmake
@@ -1,5 +1,4 @@
 set(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY OFF CACHE BOOL "")
-set(LIBCXX_HAS_WIN32_THREAD_API ON CACHE BOOL "")
 
 set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "")
 set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
diff --git a/libcxx/docs/BuildingLibcxx.rst b/libcxx/docs/BuildingLibcxx.rst
--- a/libcxx/docs/BuildingLibcxx.rst
+++ b/libcxx/docs/BuildingLibcxx.rst
@@ -159,7 +159,6 @@
           -DCMAKE_C_COMPILER=clang                                                    \
           -DCMAKE_CXX_COMPILER=clang++                                                \
           -DLLVM_ENABLE_RUNTIMES=libcxx                                               \
-          -DLIBCXX_HAS_WIN32_THREAD_API=ON                                            \
           -DLIBCXX_CXX_ABI=libstdc++                                                  \
           -DLIBCXX_TARGET_INFO="libcxx.test.target_info.MingwLocalTI"
   > ninja -C build cxx