diff --git a/include/fmt/os.h b/include/fmt/os.h
index 88151006..d44ea0c9 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -388,7 +388,7 @@ class ostream final : private detail::buffer<char> {
     clear();
   }
 
-  void grow(size_t) final;
+  FMT_API void grow(size_t) override final;
 
   ostream(cstring_view path, const detail::ostream_params& params)
       : file_(path, params.oflag) {