diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -572,8 +572,8 @@
                                                           -Werror=return-type -Wextra-semi -Wundef
                                                           -Wformat-nonliteral)
   if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+    add_definitions("-Wno-user-defined-literals")
     target_add_compile_flags_if_supported(${target} PRIVATE
-      -Wno-user-defined-literals
       -Wno-covered-switch-default
       -Wno-suggest-override
     )