diff --git a/fs/bcachefs/bset.c b/fs/bcachefs/bset.c
index 59158eb6d41f..00a821f617a5 100644
--- a/fs/bcachefs/bset.c
+++ b/fs/bcachefs/bset.c
@@ -732,7 +732,7 @@ static noinline void __build_ro_aux_tree(struct btree *b, struct bset_tree *t)
 		return;
 	}
 
-	t->extra = (t->size - rounddown_pow_of_two(t->size - 1)) << 1;
+	t->extra = eytzinger1_extra(t->size - 1);
 
 	/* First we figure out where the first key in each cacheline is */
 	eytzinger1_for_each(j, t->size - 1) {