diff --git a/ChangeLog b/ChangeLog
index fdf720d..fd42b4e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,8 @@
 Changes Prior to this release
     -   Avoid segfault when parsing /proc/mdstat with auto-read-only
 	arrays.
+    -   Fix problem with failing to add devices to v.large (>4TB) arrays,
+	cause by problems with device-size overflow.
 
 Changes Prior to 2.6.4 release
     -   Make "--create --auto=mdp" work for non-standard device names.
diff --git a/Detail.c b/Detail.c
index de1f409..6199d26 100644
--- a/Detail.c
+++ b/Detail.c
@@ -191,7 +191,7 @@ int Detail(char *dev, int brief, int export, int test, char *homehost)
 				if (dsize > 0)
 					printf("  Used Dev Size : %llu%s\n",
 					       dsize,
-					 human_size((long long)array.size<<10));
+					 human_size((long long)dsize<<10));
 				else
 					printf("  Used Dev Size : unknown\n");
 			} else
diff --git a/Manage.c b/Manage.c
index f17105a..1fb8468 100644
--- a/Manage.c
+++ b/Manage.c
@@ -188,6 +188,7 @@ int Manage_subdevs(char *devname, int fd,
 	 */
 	mdu_array_info_t array;
 	mdu_disk_info_t disc;
+	unsigned long long array_size;
 	mddev_dev_t dv, next = NULL;
 	struct stat stb;
 	int j, jnext = 0;
@@ -202,6 +203,14 @@ int Manage_subdevs(char *devname, int fd,
 		return 1;
 	}
 
+	/* array.size is only 32 bit and may be truncated.
+	 * So read from sysfs if possible, and record number of sectors
+	 */
+
+	array_size = get_component_size(fd);
+	if (array_size <= 0)
+		array_size = array.size * 2;
+
 	tst = super_by_fd(fd);
 	if (!tst) {
 		fprintf(stderr, Name ": unsupport array - version %d.%d\n",
@@ -337,7 +346,7 @@ int Manage_subdevs(char *devname, int fd,
 
 				/* Make sure device is large enough */
 				if (tst->ss->avail_size(tst, ldsize/512) <
-				    array.size) {
+				    array_size) {
 					fprintf(stderr, Name ": %s not large enough to join array\n",
 						dv->devname);
 					return 1;
@@ -412,7 +421,7 @@ int Manage_subdevs(char *devname, int fd,
 				/* non-persistent. Must ensure that new drive
 				 * is at least array.size big.
 				 */
-				if (ldsize/512 < array.size) {
+				if (ldsize/512 < array_size) {
 					fprintf(stderr, Name ": %s not large enough to join array\n",
 						dv->devname);
 					return 1;