--- usr.sbin/iovctl/iovctl.c.orig	2017-09-06 12:53:35.000000000 +0200
+++ usr.sbin/iovctl/iovctl.c	2017-09-06 12:57:33.000000000 +0200
@@ -230,17 +230,21 @@
 		usage();
 	}
 
-	if (device == NULL && filename == NULL) {
+	if (device == NULL && filename == NULL  && action != CONFIG) {
 		warnx("Either the -d or -f flag must be specified");
 		usage();
 	}
 
 	switch (action) {
 	case CONFIG:
-		if (filename == NULL) {
+		if (device != NULL) {
 			warnx("-d flag cannot be used with the -C flag");
 			usage();
 		}
+		if (filename == NULL) {
+			warnx("The -f flag must be specified");
+			usage();
+		}
 		config_action(filename, dryrun);
 		break;
 	case DELETE: