diff --git a/src/internal/tpax_driver_impl.h b/src/internal/tpax_driver_impl.h
index 5775900..5fabb0a 100644
--- a/src/internal/tpax_driver_impl.h
+++ b/src/internal/tpax_driver_impl.h
@@ -84,10 +84,7 @@ struct tpax_unit_ctx_impl {
 	off_t			dpos;
 	const char *		link;
 	char			linkbuf[1024];
-	union {
-		struct tpax_ustar_header uhdr;
-		struct tpax_cpio_header  chdr;
-	} hdrbufs;
+	size_t			hdrbuf[];
 };