diff --git a/board/src/piece_sets.rs b/board/src/piece_sets.rs
index f7435e5..46f0164 100644
--- a/board/src/piece_sets.rs
+++ b/board/src/piece_sets.rs
@@ -3,10 +3,11 @@
 mod bitboards;
 mod mailbox;
 
+pub(crate) use mailbox::Mailbox;
+
 use bitboards::{ByColor, ByColorAndShape};
 use chessfriend_bitboard::BitBoard;
 use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
-use mailbox::Mailbox;
 
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum PlacePieceStrategy {
@@ -52,7 +53,7 @@ impl PieceSet {
             for s in Shape::into_iter() {
                 let bitboard = pieces[c as usize][s as usize];
                 for square in bitboard.occupied_squares() {
-                    mailbox.set(square, Piece::new(c, s));
+                    mailbox.set(Piece::new(c, s), square);
                 }
             }
         }
@@ -114,7 +115,7 @@ impl PieceSet {
         let piece: Piece = piece.into();
         self.by_color_and_shape.set_square(square, piece);
         self.by_color.set_square(square, color);
-        self.mailbox.set(square, piece);
+        self.mailbox.set(piece, square);
 
         Ok(PlacedPiece::new(piece, square))
     }
@@ -123,7 +124,7 @@ impl PieceSet {
         if let Some(piece) = self.mailbox.get(square) {
             self.by_color_and_shape.clear_square(square, piece.into());
             self.by_color.clear_square(square, piece.color());
-            self.mailbox.clear(square);
+            self.mailbox.remove(square);
 
             Some(PlacedPiece::new(piece, square))
         } else {