diff --git a/src/logic/future_moves.rs b/src/logic/future_moves.rs
index 5c05b3f..7d51d50 100644
--- a/src/logic/future_moves.rs
+++ b/src/logic/future_moves.rs
@@ -343,12 +343,9 @@ impl FutureMoves {
                 }
 
                 node.children.retain_mut(|c| {
-                    if let Some(new_c) = index_map[*c] {
-                        *c = new_c;
-                        true
-                    } else {
-                        panic!("node is not kept in move");
-                    }
+                    debug_assert!(index_map.get(*c).unwrap().is_some());
+                    *c = unsafe { index_map.get_unchecked(*c).unwrap_unchecked() };
+                    true
                 });
 
                 node
@@ -358,3 +355,75 @@ impl FutureMoves {
         self.current_root = index_map[root];
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn prune_tree_test() {
+        let mut futm = FutureMoves::new(Piece::Black, 0, 0);
+        futm.arena.push(Move {
+            i: 0,
+            j: 0,
+            board: Board::new(),
+            winner: Winner::None,
+            parent: None,
+            children: vec![1, 3, 4],
+            value: 0,
+            self_value: 0,
+            color: Piece::Black,
+            lazy_children: false,
+        });
+
+        futm.current_root = Some(0);
+
+        // child 1
+        futm.arena.push(Move::new(
+            0,
+            0,
+            Board::new(),
+            Piece::White,
+            false,
+            Piece::Black,
+            Some(0),
+        ));
+
+        // dummy
+        futm.arena.push(Move::new(
+            1234,
+            1234,
+            Board::new(),
+            Piece::White,
+            false,
+            Piece::Black,
+            None,
+        ));
+
+        futm.arena.push(Move::new(
+            0,
+            0,
+            Board::new(),
+            Piece::White,
+            false,
+            Piece::Black,
+            Some(0),
+        ));
+        futm.arena.push(Move::new(
+            0,
+            0,
+            Board::new(),
+            Piece::White,
+            false,
+            Piece::Black,
+            Some(0),
+        ));
+        assert_eq!(futm.arena_len(), 5);
+
+        futm.refocus_tree();
+        assert_eq!(futm.arena_len(), 4, "{:?}", futm.arena);
+        assert_eq!(futm.arena[0].children.len(), 3);
+
+        assert_ne!(futm.arena[2].i, 1234, "dummy value still exists");
+    }
+}