diff --git a/mapfile.c b/mapfile.c
index 6b2207d..ac35176 100644
--- a/mapfile.c
+++ b/mapfile.c
@@ -292,6 +292,10 @@ struct map_ent *map_by_uuid(struct map_ent **map, int uuid[4])
 struct map_ent *map_by_devnm(struct map_ent **map, char *devnm)
 {
 	struct map_ent *mp;
+
+	if (!devnm)
+		return NULL;
+
 	if (!*map)
 		map_read(map);
 
diff --git a/util.c b/util.c
index 9cd89fa..8c7f3fd 100644
--- a/util.c
+++ b/util.c
@@ -1160,6 +1160,11 @@ struct supertype *super_by_fd(int fd, char **subarrayp)
 	int i;
 	char *subarray = NULL;
 	char container[32] = "";
+	char *devnm = NULL;
+
+	devnm = fd2devnm(fd);
+	if (!devnm)
+		return NULL;
 
 	sra = sysfs_read(fd, NULL, GET_VERSION);
 
@@ -1205,7 +1210,7 @@ struct supertype *super_by_fd(int fd, char **subarrayp)
 		if (subarrayp)
 			*subarrayp = subarray;
 		strcpy(st->container_devnm, container);
-		strcpy(st->devnm, fd2devnm(fd));
+		strncpy(st->devnm, devnm, MD_NAME_MAX - 1);
 	} else
 		free(subarray);