diff --git a/sys/dev/isp/ispmbox.h b/sys/dev/isp/ispmbox.h
index a517ece47c6..7a787fda1e7 100644
--- a/sys/dev/isp/ispmbox.h
+++ b/sys/dev/isp/ispmbox.h
@@ -564,7 +564,7 @@ typedef struct {
 	u_int16_t	pdb_options;
 	u_int8_t	pdb_mstate;
 	u_int8_t	pdb_sstate;
-#define	BITS2WORD(x)	(x)[0] << 16 | (x)[3] << 8 | (x)[2]
+#define	BITS2WORD(x)	((x)[0] << 16 | (x)[3] << 8 | (x)[2])
 	u_int8_t	pdb_hardaddr_bits[4];
 	u_int8_t	pdb_portid_bits[4];
 	u_int8_t	pdb_nodename[8];