diff --git a/src/main.rs b/src/main.rs
index 4b91d9c28..f7b3dc508 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -15,7 +15,8 @@ use crate::lines::{
 };
 use crate::parse::{find_lang, parse, parse_lines, read_or_die, ConfigDir};
 use crate::style::apply_colors;
-use crate::tree_diff::{change_positions, mark_nodes};
+use crate::tree_diff::{change_positions, mark_nodes, set_next};
+use crate::ucs::{toplevel_list, mark_node};
 
 fn term_width() -> Option<usize> {
     term_size::dimensions().map(|(w, _)| w)
@@ -83,10 +84,13 @@ fn main() {
         None => (parse_lines(&arena, &lhs_src), parse_lines(&arena, &rhs_src)),
     };
 
-    mark_nodes(&lhs, &rhs);
+    let (lhs, rhs) = toplevel_list(&arena, lhs, rhs);
+    set_next(lhs);
+    set_next(rhs);
+    mark_node(lhs, rhs);
 
-    let lhs_positions = change_positions(&lhs_src, &rhs_src, &lhs);
-    let rhs_positions = change_positions(&rhs_src, &lhs_src, &rhs);
+    let lhs_positions = change_positions(&lhs_src, &rhs_src, &[lhs]);
+    let rhs_positions = change_positions(&rhs_src, &lhs_src, &[rhs]);
 
     let mut groups = visible_groups(&lhs_positions, &rhs_positions);
     for group in &mut groups {
diff --git a/src/ucs.rs b/src/ucs.rs
index 134440971..571dd5a4e 100644
--- a/src/ucs.rs
+++ b/src/ucs.rs
@@ -6,6 +6,7 @@ use std::collections::{BinaryHeap, HashMap};
 use std::hash::{Hash, Hasher};
 
 use crate::tree_diff::{ChangeKind, Node};
+use typed_arena::Arena;
 use Edge::*;
 
 #[derive(Debug, Clone)]
@@ -299,7 +300,17 @@ fn neighbours<'a>(v: &Vertex<'a>) -> Vec<(Edge, Vertex<'a>)> {
     res
 }
 
-pub fn mark_nodes<'a>(lhs: &'a Node<'a>, rhs: &'a Node<'a>) {
+pub fn toplevel_list<'a>(
+    arena: &'a Arena<Node<'a>>,
+    lhs_children: Vec<&'a Node<'a>>,
+    rhs_children: Vec<&'a Node<'a>>,
+) -> (&'a Node<'a>, &'a Node<'a>) {
+    let lhs = Node::new_list(arena, "".into(), vec![], lhs_children, "".into(), vec![]);
+    let rhs = Node::new_list(arena, "".into(), vec![], rhs_children, "".into(), vec![]);
+    (lhs, rhs)
+}
+
+pub fn mark_node<'a>(lhs: &'a Node<'a>, rhs: &'a Node<'a>) {
     let start = Vertex::new(lhs, rhs);
     let route = find_route(start);
     mark_route(&route);