diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4583f07635716b..1b6cd937f214fe 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1141,7 +1141,7 @@ static noinline int cow_file_range(struct inode *inode,
 	 */
 	if (extent_reserved) {
 		extent_clear_unlock_delalloc(inode, start,
-					     start + cur_alloc_size,
+					     start + cur_alloc_size - 1,
 					     locked_page,
 					     clear_bits,
 					     page_ops);