diff --git a/Create.c b/Create.c
index bbf2f2b..337040c 100644
--- a/Create.c
+++ b/Create.c
@@ -672,7 +672,7 @@ int Create(struct supertype *st, char *mddev,
 
 	sysfs_init(&info, mdfd, 0);
 
-	if (st->ss->external && st->subarray[0]) {
+	if (st->ss->external && st->container_dev != NoMdDev) {
 		/* member */
 
 		/* When creating a member, we need to be careful
@@ -775,7 +775,8 @@ int Create(struct supertype *st, char *mddev,
 				if (have_container)
 					fd = -1;
 				else {
-					if (st->ss->external && st->subarray[0])
+					if (st->ss->external &&
+					    st->container_dev != NoMdDev)
 						fd = open(dv->devname, O_RDWR);
 					else
 						fd = open(dv->devname, O_RDWR|O_EXCL);
@@ -906,7 +907,7 @@ int Create(struct supertype *st, char *mddev,
 		}
 		if (verbose >= 0)
 			fprintf(stderr, Name ": array %s started.\n", mddev);
-		if (st->ss->external && st->subarray[0]) {
+		if (st->ss->external && st->container_dev != NoMdDev) {
 			if (need_mdmon)
 				start_mdmon(st->container_dev);
 
diff --git a/super-ddf.c b/super-ddf.c
index ab35891..01c376d 100644
--- a/super-ddf.c
+++ b/super-ddf.c
@@ -893,6 +893,7 @@ static struct supertype *match_metadata_desc_ddf(char *arg)
 
 	st = malloc(sizeof(*st));
 	memset(st, 0, sizeof(*st));
+	st->container_dev = NoMdDev;
 	st->ss = &super_ddf;
 	st->max_devs = 512;
 	st->minor_version = 0;
diff --git a/super-intel.c b/super-intel.c
index 3c18e57..5470c91 100644
--- a/super-intel.c
+++ b/super-intel.c
@@ -333,6 +333,7 @@ static struct supertype *match_metadata_desc_imsm(char *arg)
 	if (!st)
 		return NULL;
 	memset(st, 0, sizeof(*st));
+	st->container_dev = NoMdDev;
 	st->ss = &super_imsm;
 	st->max_devs = IMSM_MAX_DEVICES;
 	st->minor_version = 0;
diff --git a/super0.c b/super0.c
index 74b05ae..1fcdd24 100644
--- a/super0.c
+++ b/super0.c
@@ -917,6 +917,7 @@ static struct supertype *match_metadata_desc0(char *arg)
 	if (!st) return st;
 
 	memset(st, 0, sizeof(*st));
+	st->container_dev = NoMdDev;
 	st->ss = &super0;
 	st->info = NULL;
 	st->minor_version = 90;
diff --git a/super1.c b/super1.c
index ca2a54e..6974daa 100644
--- a/super1.c
+++ b/super1.c
@@ -1371,6 +1371,7 @@ static struct supertype *match_metadata_desc1(char *arg)
 	if (!st) return st;
 
 	memset(st, 0, sizeof(*st));
+	st->container_dev = NoMdDev;
 	st->ss = &super1;
 	st->max_devs = 384;
 	st->sb = NULL;
diff --git a/util.c b/util.c
index 83a972e..57b7e1f 100644
--- a/util.c
+++ b/util.c
@@ -1126,6 +1126,9 @@ struct supertype *guess_super_type(int fd, enum guess_types guess_type)
 	int i;
 
 	st = malloc(sizeof(*st));
+	memset(st, 0, sizeof(*st));
+	st->container_dev = NoMdDev;
+
 	for (i=0 ; superlist[i]; i++) {
 		int rv;
 		ss = superlist[i];