diff --git a/src/node/node_modifier.rs b/src/node/node_modifier.rs
index c748d7e..19dcfb3 100644
--- a/src/node/node_modifier.rs
+++ b/src/node/node_modifier.rs
@@ -13,6 +13,9 @@ impl<'a> NodeModifier<'a> {
         let mut selected = root;
         while random_range(0..PICK_STOP_PROBABILITY) == PICK_STOP_PROBABILITY - 1 {
             let len = selected.children.len();
+            if len == 0 {
+                break;
+            }
             selected = &mut selected.children[random_range(0..len)];
         }
         NodeModifier {
@@ -34,4 +37,6 @@ impl<'a> NodeModifier<'a> {
         node.children.push(moved);
         self.picked_node.children.insert(operated_index, node);
     }
+
+    pub fn mutate_node(&mut self) {}
 }