diff --git a/libcxx/cmake/Modules/CheckLibcxxAtomic.cmake b/libcxx/cmake/Modules/CheckLibcxxAtomic.cmake
--- a/libcxx/cmake/Modules/CheckLibcxxAtomic.cmake
+++ b/libcxx/cmake/Modules/CheckLibcxxAtomic.cmake
@@ -34,10 +34,12 @@
 # Perform the check for 64bit atomics without libatomic. It may have been
 # added to the required libraries during in the configuration of LLVM, which
 # would cause the check for CXX atomics without libatomic to incorrectly pass.
-set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
-list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "atomic")
-check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
-set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+if (CMAKE_REQUIRED_LIBRARIES)
+  set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
+  list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "atomic")
+  check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
+  set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+endif()
 
 check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
 # If not, check if the library exists, and atomics work with it.