diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 95944b8..6bf16d5 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3297,6 +3297,9 @@
 }
 
 /* extent-tree.c */
+
+u64 btrfs_csum_bytes_to_leaves(struct btrfs_root *root, u64 csum_bytes);
+
 static inline u64 btrfs_calc_trans_metadata_size(struct btrfs_root *root,
 						 unsigned num_items)
 {