diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S
index b22cbab3..90ddd106 100644
--- a/src/arch/i386/prefix/romprefix.S
+++ b/src/arch/i386/prefix/romprefix.S
@@ -123,6 +123,7 @@ undiheader:
 	.word	_data16_size		/* Stack segment size */
 	.word	_data16_size		/* Data segment size */
 	.word	_text16_size		/* Code segment size */
+	.ascii	"PCIR"			/* Bus type */
 	.equ undiheader_len, . - undiheader
 	.size undiheader, . - undiheader