diff --git a/lib/libarchive/archive.h.in b/lib/libarchive/archive.h.in
index 03fbd4cda43..24be2de4ffd 100644
--- a/lib/libarchive/archive.h.in
+++ b/lib/libarchive/archive.h.in
@@ -291,7 +291,8 @@ int		 archive_write_open_file(struct archive *, const char *_file);
  */
 int		 archive_write_header(struct archive *,
 		     struct archive_entry *);
-ssize_t		 archive_write_data(struct archive *, const void *, size_t);
+/* TODO: should be ssize_t, but that might require .so version bump? */
+int		 archive_write_data(struct archive *, const void *, size_t);
 int		 archive_write_close(struct archive *);
 void		 archive_write_finish(struct archive *);