diff --git a/lib/libarchive/archive.h.in b/lib/libarchive/archive.h.in
index 52603437eb6..03fbd4cda43 100644
--- a/lib/libarchive/archive.h.in
+++ b/lib/libarchive/archive.h.in
@@ -291,7 +291,7 @@ int		 archive_write_open_file(struct archive *, const char *_file);
  */
 int		 archive_write_header(struct archive *,
 		     struct archive_entry *);
-int		 archive_write_data(struct archive *, const void *, size_t);
+ssize_t		 archive_write_data(struct archive *, const void *, size_t);
 int		 archive_write_close(struct archive *);
 void		 archive_write_finish(struct archive *);