diff --git a/src/logic/future_moves.rs b/src/logic/future_moves.rs
index a8bf47c..be1241c 100644
--- a/src/logic/future_moves.rs
+++ b/src/logic/future_moves.rs
@@ -442,22 +442,15 @@ impl FutureMoves {
         self.arena = moves
             .into_iter()
             .map(|mut node| {
-                if let Some(parent) = node.parent.as_mut() {
-                    if let Some(new_parent) = index_map[*parent] {
-                        *parent = new_parent;
-                    } else {
-                        // make sure we don't have dangling parents
-                        node.parent = None;
-                    }
-                }
+                node.parent = node
+                    .parent
+                    .and_then(|parent| index_map.get(parent).and_then(|&x| x));
 
                 for c in node.children.as_mut_slice() {
-                    debug_assert_ne!(
-                        index_map.get(*c).and_then(|&x| x),
-                        None,
-                        "index_map should contain the child's index"
-                    );
-                    *c = unsafe { index_map.get_unchecked(*c).unwrap_unchecked() };
+                    *c = index_map
+                        .get(*c)
+                        .and_then(|&x| x)
+                        .expect("index_map should contain the child's index");
                 }
 
                 node