diff --git a/llvm/utils/gn/secondary/libcxx/include/BUILD.gn b/llvm/utils/gn/secondary/libcxx/include/BUILD.gn
index d4a30c6bd3cbb9..437881a724ddd7 100644
--- a/llvm/utils/gn/secondary/libcxx/include/BUILD.gn
+++ b/llvm/utils/gn/secondary/libcxx/include/BUILD.gn
@@ -240,6 +240,7 @@ if (current_toolchain == default_toolchain) {
       "__filesystem/recursive_directory_iterator.h",
       "__filesystem/space_info.h",
       "__filesystem/u8path.h",
+      "__format/buffer.h",
       "__format/format_arg.h",
       "__format/format_args.h",
       "__format/format_context.h",