diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 5a4a74c1097c6ce80eb38e726954304dbb25bc53..9620d452d030d1fdc413c10adaa20561b37d357b 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -255,19 +255,25 @@ static struct page *read_sb_page(mddev_t *mddev, long offset, unsigned long inde
 
 }
 
-static int write_sb_page(mddev_t *mddev, long offset, struct page *page, int wait)
+static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 {
 	mdk_rdev_t *rdev;
 	struct list_head *tmp;
+	mddev_t *mddev = bitmap->mddev;
 
 	ITERATE_RDEV(mddev, rdev, tmp)
 		if (test_bit(In_sync, &rdev->flags)
-		    && !test_bit(Faulty, &rdev->flags))
+		    && !test_bit(Faulty, &rdev->flags)) {
+			int size = PAGE_SIZE;
+			if (page->index == bitmap->file_pages-1)
+				size = roundup(bitmap->last_page_size,
+					       bdev_hardsect_size(rdev->bdev));
 			md_super_write(mddev, rdev,
-				       (rdev->sb_offset<<1) + offset
+				       (rdev->sb_offset<<1) + bitmap->offset
 				       + page->index * (PAGE_SIZE/512),
-				       PAGE_SIZE,
+				       size,
 				       page);
+		}
 
 	if (wait)
 		md_super_wait(mddev);
@@ -282,7 +288,7 @@ static int write_page(struct bitmap *bitmap, struct page *page, int wait)
 	struct buffer_head *bh;
 
 	if (bitmap->file == NULL)
-		return write_sb_page(bitmap->mddev, bitmap->offset, page, wait);
+		return write_sb_page(bitmap, page, wait);
 
 	bh = page_buffers(page);
 
@@ -923,6 +929,7 @@ static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
 			}
 
 			bitmap->filemap[bitmap->file_pages++] = page;
+			bitmap->last_page_size = count;
 		}
 		paddr = kmap_atomic(page, KM_USER0);
 		if (bitmap->flags & BITMAP_HOSTENDIAN)
diff --git a/include/linux/raid/bitmap.h b/include/linux/raid/bitmap.h
index 6db9a4c153556a7236caf4dbf376b27900af3f15..dd5a05d03d4f477f2c90040331ec6d8c7de03d36 100644
--- a/include/linux/raid/bitmap.h
+++ b/include/linux/raid/bitmap.h
@@ -232,6 +232,7 @@ struct bitmap {
 	struct page **filemap; /* list of cache pages for the file */
 	unsigned long *filemap_attr; /* attributes associated w/ filemap pages */
 	unsigned long file_pages; /* number of pages in the file */
+	int last_page_size; /* bytes in the last page */
 
 	unsigned long flags;