diff --git a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
--- a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
+++ b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -278,6 +278,8 @@
       foreach(type ${flag_types})
         list(APPEND cmake_args ${${type}_flag})
       endforeach()
+    else()
+      set(cmake_args ${ARG_CMAKE_ARGS})
     endif()
   else()
     set(llvm_config_path "$<TARGET_FILE:llvm-config>")