diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 7c5e3d40657412..c7ed30edf1cd40 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -474,7 +474,7 @@ int btrfs_dirty_pages(struct btrfs_inode *inode, struct page **pages,
 	loff_t isize = i_size_read(&inode->vfs_inode);
 	unsigned int extra_bits = 0;
 
-	start_pos = pos & ~((u64) fs_info->sectorsize - 1);
+	start_pos = round_down(pos, fs_info->sectorsize);
 	num_bytes = round_up(write_bytes + pos - start_pos,
 			     fs_info->sectorsize);