diff --git a/btrfstune.c b/btrfstune.c
index 257bac44..0a6ad9ca 100644
--- a/btrfstune.c
+++ b/btrfstune.c
@@ -149,7 +149,7 @@ static int change_extents_uuid(struct btrfs_fs_info *fs_info)
 			goto next;
 
 		bytenr = key.objectid;
-		eb = read_tree_block(root, bytenr, root->nodesize, 0);
+		eb = read_tree_block(root, bytenr, root->fs_info->nodesize, 0);
 		if (IS_ERR(eb)) {
 			error("failed to read tree block: %llu", bytenr);
 			ret = PTR_ERR(eb);