diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 7b38d06..cc2eada 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -126,6 +126,7 @@
 struct btrfs_bio_stripe {
 	struct btrfs_device *dev;
 	u64 physical;
+	u64 length; /* only used for discard mappings */
 };
 
 struct btrfs_multi_bio {