diff --git a/Manage.c b/Manage.c
index 8297708..7b3fabe 100644
--- a/Manage.c
+++ b/Manage.c
@@ -349,14 +349,6 @@ int Manage_subdevs(char *devname, int fd,
 
 			if (array.not_persistent == 0) {
 
-				/* Make sure device is large enough */
-				if (tst->ss->avail_size(tst, ldsize/512) <
-				    array_size) {
-					fprintf(stderr, Name ": %s not large enough to join array\n",
-						dv->devname);
-					return 1;
-				}
-
 				/* need to find a sample superblock to copy, and
 				 * a spare slot to use
 				 */
@@ -386,6 +378,15 @@ int Manage_subdevs(char *devname, int fd,
 					fprintf(stderr, Name ": cannot find valid superblock in this array - HELP\n");
 					return 1;
 				}
+
+				/* Make sure device is large enough */
+				if (tst->ss->avail_size(tst, ldsize/512) <
+				    array_size) {
+					fprintf(stderr, Name ": %s not large enough to join array\n",
+						dv->devname);
+					return 1;
+				}
+
 				/* Possibly this device was recently part of the array
 				 * and was temporarily removed, and is now being re-added.
 				 * If so, we can simply re-add it.
diff --git a/bitmap.c b/bitmap.c
index fdf8884..b647939 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -115,6 +115,15 @@ unsigned long long bitmap_bits(unsigned long long array_size,
 	return (array_size * 512 + chunksize - 1) / chunksize;
 }
 
+unsigned long bitmap_sectors(struct bitmap_super_s *bsb)
+{
+	unsigned long long bits = bitmap_bits(__le64_to_cpu(bsb->sync_size),
+					      __le32_to_cpu(bsb->chunksize));
+	int bits_per_sector = 8*512;
+	return (bits + bits_per_sector - 1) / bits_per_sector;
+}
+
+
 bitmap_info_t *bitmap_fd_read(int fd, int brief)
 {
 	/* Note: fd might be open O_DIRECT, so we must be
diff --git a/mdadm.h b/mdadm.h
index 5c18d15..ce140e5 100644
--- a/mdadm.h
+++ b/mdadm.h
@@ -474,6 +474,7 @@ extern int CreateBitmap(char *filename, int force, char uuid[16],
 			int major);
 extern int ExamineBitmap(char *filename, int brief, struct supertype *st);
 extern int bitmap_update_uuid(int fd, int *uuid, int swap);
+extern unsigned long bitmap_sectors(struct bitmap_super_s *bsb);
 
 extern int md_get_version(int fd);
 extern int get_linux_version(void);
diff --git a/super1.c b/super1.c
index fe915f8..e1d0219 100644
--- a/super1.c
+++ b/super1.c
@@ -1214,10 +1214,21 @@ static struct supertype *match_metadata_desc1(char *arg)
  */
 static __u64 avail_size1(struct supertype *st, __u64 devsize)
 {
+	struct mdp_superblock_1 *super = st->sb;
 	if (devsize < 24)
 		return 0;
 
-	devsize -= choose_bm_space(devsize);
+	if (super == NULL)
+		/* creating:  allow suitable space for bitmap */
+		devsize -= choose_bm_space(devsize);
+#ifndef MDASSEMBLE
+	else if (__le32_to_cpu(super->feature_map)&MD_FEATURE_BITMAP_OFFSET) {
+		/* hot-add. allow for actual size of bitmap */
+		struct bitmap_super_s *bsb;
+		bsb = (struct bitmap_super_s *)(((char*)super)+1024);
+		devsize -= bitmap_sectors(bsb);
+	}
+#endif
 
 	switch(st->minor_version) {
 	case -1: /* no specified.  Now time to set default */