diff --git a/toolsrc/CMakeLists.txt b/toolsrc/CMakeLists.txt
index bbecb8f30..9106204b2 100644
--- a/toolsrc/CMakeLists.txt
+++ b/toolsrc/CMakeLists.txt
@@ -38,6 +38,10 @@ If you would like to try anyway, pass --allowAppleClang to bootstrap.sh.")
     endif()
 elseif(CMAKE_CXX_COMPILER_ID MATCHES "[Cc]lang")
     set(CLANG 1)
+    if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "9.0.0")
+        set(NO_LIBCXXFS 1)
+        add_compile_definitions(_LIBCPP_NO_EXPERIMENTAL_DEPRECATION_WARNING_FILESYSTEM=1)
+    endif()
 elseif(NOT MSVC)
     message(FATAL_ERROR "Unknown compiler: ${CMAKE_CXX_COMPILER_ID}")
 endif()