diff --git a/board/src/piece_sets/mailbox.rs b/board/src/piece_sets/mailbox.rs
index 05cdf9b..ce11cf0 100644
--- a/board/src/piece_sets/mailbox.rs
+++ b/board/src/piece_sets/mailbox.rs
@@ -3,7 +3,7 @@
 use chessfriend_core::{Piece, PlacedPiece, Square};
 use std::iter::FromIterator;
 
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub(crate) struct Mailbox([Option<Piece>; Square::NUM]);
 
 impl Mailbox {