diff --git a/src/batch.rs b/src/batch.rs
index a6ab818..dc019c3 100644
--- a/src/batch.rs
+++ b/src/batch.rs
@@ -240,7 +240,7 @@ impl Batch {
         item: &Item,
         online: bool,
         forward: bool,
-        agents: &mut HashMap<Index, Agent>,
+        agents: &HashMap<Index, Agent>,
     ) -> Player {
         let r = &agents[&item.agent].player;