diff --git a/include/dwarfs/writer/filesystem_writer.h b/include/dwarfs/writer/filesystem_writer.h
index 68b7731d..b62489ef 100644
--- a/include/dwarfs/writer/filesystem_writer.h
+++ b/include/dwarfs/writer/filesystem_writer.h
@@ -65,7 +65,7 @@ class filesystem_writer {
 
   internal::filesystem_writer_detail& get_internal() { return *impl_; }
 
- protected:
+ private:
   std::unique_ptr<internal::filesystem_writer_detail> impl_;
 };