diff --git a/usr.sbin/config/config.h b/usr.sbin/config/config.h
index 6c524f5e8fe5..e0504cc87878 100644
--- a/usr.sbin/config/config.h
+++ b/usr.sbin/config/config.h
@@ -125,6 +125,8 @@ struct device {
 	int	d_disabled;		/* nonzero to skip probe/attach */
 	char	*d_port;		/* io port base manifest constant */
 	int	d_portn;	/* io port base (if number not manifest) */
+#define PORT_AUTO -1    /* automatically configured */
+#define PORT_NONE -2    /* no port */
 	char	*d_mask;		/* interrupt mask */
 	int	d_maddr;		/* io memory base */
 	int	d_msize;		/* io memory size */
diff --git a/usr.sbin/config/config.y b/usr.sbin/config/config.y
index c35127c49cf8..fc396b744d1f 100644
--- a/usr.sbin/config/config.y
+++ b/usr.sbin/config/config.y
@@ -618,9 +618,9 @@ Info:
 	PORT NUMBER
 	      = { cur.d_portn = $2; } |
 	PORT AUTO
-	      = { cur.d_portn = -1; } |
+	      = { cur.d_portn = PORT_AUTO; } |
 	PORT NONE
-	      = { cur.d_portn = -2; } |
+	      = { cur.d_portn = PORT_NONE; } |
 	TTY 
 	      = { cur.d_mask = "tty"; } |
 	BIO 
@@ -907,7 +907,7 @@ init_dev(dp)
 	dp->d_pri = -1;
 	dp->d_slave = dp->d_lun = dp->d_target = dp->d_drive = dp->d_unit = UNKNOWN;
 	dp->d_port = (char *)0;
-	dp->d_portn = 0;
+	dp->d_portn = PORT_NONE;
 	dp->d_irq = -1;
 	dp->d_drq = -1;
 	dp->d_maddr = 0;
diff --git a/usr.sbin/config/mkioconf.c b/usr.sbin/config/mkioconf.c
index ac5554645536..03eb77f0acd7 100644
--- a/usr.sbin/config/mkioconf.c
+++ b/usr.sbin/config/mkioconf.c
@@ -757,8 +757,8 @@ isa_devtab(fp, table, dev_idp)
 		fprintf(fp, "{ %2d, &%3sdriver,", (*dev_idp)++, dp->d_name);
 		if (dp->d_port)
 			fprintf(fp, " %8s,", dp->d_port);
-		else if (dp->d_portn == -1 || dp->d_portn == -2)
-			fprintf(fp, "       %2d,", dp->d_portn);
+		else if (dp->d_portn == PORT_AUTO || dp->d_portn == PORT_NONE)
+			fprintf(fp, "       %d,", dp->d_portn);
 		else
 			fprintf(fp, "   0x%04x,", dp->d_portn);
 		fprintf(fp, "%6s, %2d, C 0x%05X, %5d, %8s, %3d, 0x%04X,     0,    0,       0,       0, %6d, %8d,   0 },\n",