diff --git a/resize/main.c b/resize/main.c
index 1394ae1..cf37e26 100644
--- a/resize/main.c
+++ b/resize/main.c
@@ -41,7 +41,7 @@ char *program_name, *device_name, *io_options;
 static void usage (char *prog)
 {
 	fprintf (stderr, _("Usage: %s [-d debug_flags] [-f] [-F] [-M] [-P] "
-			   "[-p] device [new_size]\n\n"), prog);
+			   "[-p] device [-b|-s|new_size]\n\n"), prog);
 
 	exit (1);
 }
@@ -199,7 +199,7 @@ int main (int argc, char ** argv)
 	if (argc && *argv)
 		program_name = *argv;
 
-	while ((c = getopt (argc, argv, "d:fFhMPpS:")) != EOF) {
+	while ((c = getopt(argc, argv, "d:fFhMPpS:bs")) != EOF) {
 		switch (c) {
 		case 'h':
 			usage(program_name);
@@ -225,6 +225,12 @@ int main (int argc, char ** argv)
 		case 'S':
 			use_stride = atoi(optarg);
 			break;
+		case 'b':
+			flags |= RESIZE_ENABLE_64BIT;
+			break;
+		case 's':
+			flags |= RESIZE_DISABLE_64BIT;
+			break;
 		default:
 			usage(program_name);
 		}
@@ -383,6 +389,10 @@ int main (int argc, char ** argv)
 		if (sys_page_size > fs->blocksize)
 			new_size &= ~((sys_page_size / fs->blocksize)-1);
 	}
+	/* If changing 64bit, don't change the filesystem size. */
+	if (flags & (RESIZE_DISABLE_64BIT | RESIZE_ENABLE_64BIT)) {
+		new_size = ext2fs_blocks_count(fs->super);
+	}
 	if (!EXT2_HAS_INCOMPAT_FEATURE(fs->super,
 				       EXT4_FEATURE_INCOMPAT_64BIT)) {
 		/* Take 16T down to 2^32-1 blocks */
@@ -434,7 +444,31 @@ int main (int argc, char ** argv)
 			fs->blocksize / 1024, new_size);
 		exit(1);
 	}
-	if (new_size == ext2fs_blocks_count(fs->super)) {
+	if ((flags & RESIZE_DISABLE_64BIT) && (flags & RESIZE_ENABLE_64BIT)) {
+		fprintf(stderr, _("Cannot set and unset 64bit feature.\n"));
+		exit(1);
+	} else if (flags & (RESIZE_DISABLE_64BIT | RESIZE_ENABLE_64BIT)) {
+		new_size = ext2fs_blocks_count(fs->super);
+		if (new_size >= (1ULL << 32)) {
+			fprintf(stderr, _("Cannot change the 64bit feature "
+				"on a filesystem that is larger than "
+				"2^32 blocks.\n"));
+			exit(1);
+		}
+		if (mount_flags & EXT2_MF_MOUNTED) {
+			fprintf(stderr, _("Cannot change the 64bit feature "
+				"while the filesystem is mounted.\n"));
+			exit(1);
+		}
+		if (flags & RESIZE_ENABLE_64BIT &&
+		    !EXT2_HAS_INCOMPAT_FEATURE(fs->super,
+				EXT3_FEATURE_INCOMPAT_EXTENTS)) {
+			fprintf(stderr, _("Please enable the extents feature "
+				"with tune2fs before enabling the 64bit "
+				"feature.\n"));
+			exit(1);
+		}
+	} else if (new_size == ext2fs_blocks_count(fs->super)) {
 		fprintf(stderr, _("The filesystem is already %llu blocks "
 			"long.  Nothing to do!\n\n"), new_size);
 		exit(0);
diff --git a/resize/resize2fs.8.in b/resize/resize2fs.8.in
index a1f3099..1c75816 100644
--- a/resize/resize2fs.8.in
+++ b/resize/resize2fs.8.in
@@ -8,7 +8,7 @@ resize2fs \- ext2/ext3/ext4 file system resizer
 .SH SYNOPSIS
 .B resize2fs
 [
-.B \-fFpPM
+.B \-fFpPMbs
 ]
 [
 .B \-d
@@ -85,8 +85,21 @@ to shrink the size of filesystem.  Then you may use
 to shrink the size of the partition.  When shrinking the size of
 the partition, make sure you do not make it smaller than the new size
 of the ext2 filesystem!
+.PP
+The
+.B \-b
+and
+.B \-s
+options enable and disable the 64bit feature, respectively.  The resize2fs
+program will, of course, take care of resizing the block group descriptors
+and moving other data blocks out of the way, as needed.  It is not possible
+to resize the filesystem concurrent with changing the 64bit status.
 .SH OPTIONS
 .TP
+.B \-b
+Turns on the 64bit feature, resizes the group descriptors as necessary, and
+moves other metadata out of the way.
+.TP
 .B \-d \fIdebug-flags
 Turns on various resize2fs debugging features, if they have been compiled
 into the binary.
@@ -126,6 +139,9 @@ of what the program is doing.
 .B \-P
 Print the minimum size of the filesystem and exit.
 .TP
+.B \-s
+Turns off the 64bit feature and frees blocks that are no longer in use.
+.TP
 .B \-S \fIRAID-stride
 The
 .B resize2fs
diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index 6c2c870..3ee8ee4 100644
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -53,6 +53,9 @@ static errcode_t ext2fs_calculate_summary_stats(ext2_filsys fs);
 static errcode_t fix_sb_journal_backup(ext2_filsys fs);
 static errcode_t mark_table_blocks(ext2_filsys fs,
 				   ext2fs_block_bitmap bmap);
+static errcode_t resize_group_descriptors(ext2_resize_t rfs, blk64_t new_size);
+static errcode_t move_bg_metadata(ext2_resize_t rfs);
+static errcode_t zero_high_bits_in_inodes(ext2_resize_t rfs);
 
 /*
  * Some helper CPP macros
@@ -119,13 +122,30 @@ errcode_t resize_fs(ext2_filsys fs, blk64_t *new_size, int flags,
 	if (retval)
 		goto errout;
 
+	init_resource_track(&rtrack, "resize_group_descriptors", fs->io);
+	retval = resize_group_descriptors(rfs, *new_size);
+	if (retval)
+		goto errout;
+	print_resource_track(rfs, &rtrack, fs->io);
+
+	init_resource_track(&rtrack, "move_bg_metadata", fs->io);
+	retval = move_bg_metadata(rfs);
+	if (retval)
+		goto errout;
+	print_resource_track(rfs, &rtrack, fs->io);
+
+	init_resource_track(&rtrack, "zero_high_bits_in_metadata", fs->io);
+	retval = zero_high_bits_in_inodes(rfs);
+	if (retval)
+		goto errout;
+	print_resource_track(rfs, &rtrack, fs->io);
+
 	init_resource_track(&rtrack, "adjust_superblock", fs->io);
 	retval = adjust_superblock(rfs, *new_size);
 	if (retval)
 		goto errout;
 	print_resource_track(rfs, &rtrack, fs->io);
 
-
 	init_resource_track(&rtrack, "fix_uninit_block_bitmaps 2", fs->io);
 	fix_uninit_block_bitmaps(rfs->new_fs);
 	print_resource_track(rfs, &rtrack, fs->io);
@@ -221,6 +241,259 @@ errout:
 	return retval;
 }
 
+/* Toggle 64bit mode */
+static errcode_t resize_group_descriptors(ext2_resize_t rfs, blk64_t new_size)
+{
+	void *o, *n, *new_group_desc;
+	dgrp_t i;
+	int copy_size;
+	errcode_t retval;
+
+	if (!(rfs->flags & (RESIZE_DISABLE_64BIT | RESIZE_ENABLE_64BIT)))
+		return 0;
+
+	if (new_size != ext2fs_blocks_count(rfs->new_fs->super) ||
+	    ext2fs_blocks_count(rfs->new_fs->super) >= (1ULL << 32) ||
+	    (rfs->flags & RESIZE_DISABLE_64BIT &&
+	     rfs->flags & RESIZE_ENABLE_64BIT))
+		return EXT2_ET_INVALID_ARGUMENT;
+
+	if (rfs->flags & RESIZE_DISABLE_64BIT) {
+		rfs->new_fs->super->s_feature_incompat &=
+				~EXT4_FEATURE_INCOMPAT_64BIT;
+		rfs->new_fs->super->s_desc_size = EXT2_MIN_DESC_SIZE;
+	} else if (rfs->flags & RESIZE_ENABLE_64BIT) {
+		rfs->new_fs->super->s_feature_incompat |=
+				EXT4_FEATURE_INCOMPAT_64BIT;
+		rfs->new_fs->super->s_desc_size = EXT2_MIN_DESC_SIZE_64BIT;
+	}
+
+	if (EXT2_DESC_SIZE(rfs->old_fs->super) ==
+	    EXT2_DESC_SIZE(rfs->new_fs->super))
+		return 0;
+
+	o = rfs->new_fs->group_desc;
+	rfs->new_fs->desc_blocks = ext2fs_div_ceil(
+			rfs->old_fs->group_desc_count,
+			EXT2_DESC_PER_BLOCK(rfs->new_fs->super));
+	retval = ext2fs_get_arrayzero(rfs->new_fs->desc_blocks,
+				      rfs->old_fs->blocksize, &new_group_desc);
+	if (retval)
+		return retval;
+
+	n = new_group_desc;
+
+	if (EXT2_DESC_SIZE(rfs->old_fs->super) <=
+	    EXT2_DESC_SIZE(rfs->new_fs->super))
+		copy_size = EXT2_DESC_SIZE(rfs->old_fs->super);
+	else
+		copy_size = EXT2_DESC_SIZE(rfs->new_fs->super);
+	for (i = 0; i < rfs->old_fs->group_desc_count; i++) {
+		memcpy(n, o, copy_size);
+		n += EXT2_DESC_SIZE(rfs->new_fs->super);
+		o += EXT2_DESC_SIZE(rfs->old_fs->super);
+	}
+
+	ext2fs_free_mem(&rfs->new_fs->group_desc);
+	rfs->new_fs->group_desc = new_group_desc;
+
+	for (i = 0; i < rfs->old_fs->group_desc_count; i++)
+		ext2fs_group_desc_csum_set(rfs->new_fs, i);
+
+	return 0;
+}
+
+/* Move bitmaps/inode tables out of the way. */
+static errcode_t move_bg_metadata(ext2_resize_t rfs)
+{
+	dgrp_t i;
+	blk64_t b, c, d;
+	ext2fs_block_bitmap old_map, new_map;
+	int old, new;
+	errcode_t retval;
+	int zero = 0, one = 1;
+
+	if (!(rfs->flags & (RESIZE_DISABLE_64BIT | RESIZE_ENABLE_64BIT)))
+		return 0;
+
+	retval = ext2fs_allocate_block_bitmap(rfs->old_fs, "oldfs", &old_map);
+	if (retval)
+		return retval;
+
+	retval = ext2fs_allocate_block_bitmap(rfs->new_fs, "newfs", &new_map);
+	if (retval)
+		goto out;
+
+	/* Construct bitmaps of super/descriptor blocks in old and new fs */
+	for (i = 0; i < rfs->old_fs->group_desc_count; i++) {
+		retval = ext2fs_super_and_bgd_loc2(rfs->old_fs, i, &b, &c, &d,
+						   NULL);
+		if (retval)
+			goto out;
+		ext2fs_mark_block_bitmap2(old_map, b);
+		ext2fs_mark_block_bitmap2(old_map, c);
+		ext2fs_mark_block_bitmap2(old_map, d);
+
+		retval = ext2fs_super_and_bgd_loc2(rfs->new_fs, i, &b, &c, &d,
+						   NULL);
+		if (retval)
+			goto out;
+		ext2fs_mark_block_bitmap2(new_map, b);
+		ext2fs_mark_block_bitmap2(new_map, c);
+		ext2fs_mark_block_bitmap2(new_map, d);
+	}
+
+	/* Find changes in block allocations for bg metadata */
+	for (b = 0;
+	     b < ext2fs_blocks_count(rfs->new_fs->super);
+	     b += EXT2FS_CLUSTER_RATIO(rfs->new_fs)) {
+		old = ext2fs_test_block_bitmap2(old_map, b);
+		new = ext2fs_test_block_bitmap2(new_map, b);
+
+		if (old && !new)
+			ext2fs_unmark_block_bitmap2(rfs->new_fs->block_map, b);
+		else if (!old && new)
+			; /* empty ext2fs_mark_block_bitmap2(new_map, b); */
+		else
+			ext2fs_unmark_block_bitmap2(new_map, b);
+	}
+	/* new_map now shows blocks that have been newly allocated. */
+
+	/* Move any conflicting bitmaps and inode tables */
+	for (i = 0; i < rfs->old_fs->group_desc_count; i++) {
+		b = ext2fs_block_bitmap_loc(rfs->new_fs, i);
+		if (ext2fs_test_block_bitmap2(new_map, b))
+			ext2fs_block_bitmap_loc_set(rfs->new_fs, i, 0);
+
+		b = ext2fs_inode_bitmap_loc(rfs->new_fs, i);
+		if (ext2fs_test_block_bitmap2(new_map, b))
+			ext2fs_inode_bitmap_loc_set(rfs->new_fs, i, 0);
+
+		c = ext2fs_inode_table_loc(rfs->new_fs, i);
+		for (b = 0; b < rfs->new_fs->inode_blocks_per_group; b++) {
+			if (ext2fs_test_block_bitmap2(new_map, b + c)) {
+				ext2fs_inode_table_loc_set(rfs->new_fs, i, 0);
+				break;
+			}
+		}
+	}
+
+out:
+	if (old_map)
+		ext2fs_free_block_bitmap(old_map);
+	if (new_map)
+		ext2fs_free_block_bitmap(new_map);
+	return retval;
+}
+
+/* Zero out the high bits of extent fields */
+static errcode_t zero_high_bits_in_extents(ext2_filsys fs, ext2_ino_t ino,
+				 struct ext2_inode *inode)
+{
+	ext2_extent_handle_t	handle;
+	struct ext2fs_extent	extent;
+	int			op = EXT2_EXTENT_ROOT;
+	errcode_t		errcode;
+
+	if (!(inode->i_flags & EXT4_EXTENTS_FL))
+		return 0;
+
+	errcode = ext2fs_extent_open(fs, ino, &handle);
+	if (errcode)
+		return errcode;
+
+	while (1) {
+		errcode = ext2fs_extent_get(handle, op, &extent);
+		if (errcode)
+			break;
+
+		op = EXT2_EXTENT_NEXT_SIB;
+
+		if (extent.e_pblk > (1ULL << 32)) {
+			extent.e_pblk &= (1ULL << 32) - 1;
+			errcode = ext2fs_extent_replace(handle, 0, &extent);
+			if (errcode)
+				break;
+		}
+	}
+
+	/* Ok if we run off the end */
+	if (errcode == EXT2_ET_EXTENT_NO_NEXT)
+		errcode = 0;
+	return errcode;
+}
+
+/* Zero out the high bits of inodes. */
+static errcode_t zero_high_bits_in_inodes(ext2_resize_t rfs)
+{
+	ext2_filsys	fs = rfs->new_fs;
+	int length = EXT2_INODE_SIZE(fs->super);
+	struct ext2_inode *inode = NULL;
+	ext2_inode_scan	scan = NULL;
+	errcode_t	retval;
+	ext2_ino_t	ino;
+	blk64_t		file_acl_block;
+	int		inode_dirty;
+
+	if (!(rfs->flags & (RESIZE_DISABLE_64BIT | RESIZE_ENABLE_64BIT)))
+		return 0;
+
+	if (fs->super->s_creator_os != EXT2_OS_LINUX)
+		return 0;
+
+	retval = ext2fs_open_inode_scan(fs, 0, &scan);
+	if (retval)
+		return retval;
+
+	retval = ext2fs_get_mem(length, &inode);
+	if (retval)
+		goto out;
+
+	do {
+		retval = ext2fs_get_next_inode_full(scan, &ino, inode, length);
+		if (retval)
+			goto out;
+		if (!ino)
+			break;
+		if (!ext2fs_test_inode_bitmap2(fs->inode_map, ino))
+			continue;
+
+		/*
+		 * Here's how we deal with high block number fields:
+		 *
+		 *  - i_size_high has been been written out with i_size_lo
+		 *    since the ext2 days, so no conversion is needed.
+		 *
+		 *  - i_blocks_hi is guarded by both the huge_file feature and
+		 *    inode flags and has always been written out with
+		 *    i_blocks_lo if the feature is set.  The field is only
+		 *    ever read if both feature and inode flag are set, so
+		 *    we don't need to zero it now.
+		 *
+		 *  - i_file_acl_high can be uninitialized, so zero it if
+		 *    it isn't already.
+		 */
+		if (inode->osd2.linux2.l_i_file_acl_high) {
+			inode->osd2.linux2.l_i_file_acl_high = 0;
+			retval = ext2fs_write_inode_full(fs, ino, inode,
+							 length);
+			if (retval)
+				goto out;
+		}
+
+		retval = zero_high_bits_in_extents(fs, ino, inode);
+		if (retval)
+			goto out;
+	} while (ino);
+
+out:
+	if (inode)
+		ext2fs_free_mem(&inode);
+	if (scan)
+		ext2fs_close_inode_scan(scan);
+	return retval;
+}
+
 /*
  * Clean up the bitmaps for unitialized bitmaps
  */
@@ -444,7 +717,8 @@ retry:
 	/*
 	 * Reallocate the group descriptors as necessary.
 	 */
-	if (old_fs->desc_blocks != fs->desc_blocks) {
+	if (EXT2_DESC_SIZE(old_fs->super) == EXT2_DESC_SIZE(fs->super) &&
+	    old_fs->desc_blocks != fs->desc_blocks) {
 		retval = ext2fs_resize_mem(old_fs->desc_blocks *
 					   fs->blocksize,
 					   fs->desc_blocks * fs->blocksize,
@@ -967,7 +1241,9 @@ static errcode_t blocks_to_move(ext2_resize_t rfs)
 		new_blocks = fs->desc_blocks + fs->super->s_reserved_gdt_blocks;
 	}
 
-	if (old_blocks == new_blocks) {
+	if (EXT2_DESC_SIZE(rfs->old_fs->super) ==
+	    EXT2_DESC_SIZE(rfs->new_fs->super) &&
+	    old_blocks == new_blocks) {
 		retval = 0;
 		goto errout;
 	}
diff --git a/resize/resize2fs.h b/resize/resize2fs.h
index 52319b5..5a1c5dc 100644
--- a/resize/resize2fs.h
+++ b/resize/resize2fs.h
@@ -82,6 +82,9 @@ typedef struct ext2_sim_progress *ext2_sim_progmeter;
 #define RESIZE_PERCENT_COMPLETE		0x0100
 #define RESIZE_VERBOSE			0x0200
 
+#define RESIZE_ENABLE_64BIT		0x0400
+#define RESIZE_DISABLE_64BIT		0x0800
+
 /*
  * This structure is used for keeping track of how much resources have
  * been used for a particular resize2fs pass.
