diff --git a/lib/classes/position.dart b/lib/classes/position.dart
index 7d28e81..e36a545 100644
--- a/lib/classes/position.dart
+++ b/lib/classes/position.dart
@@ -217,7 +217,7 @@ class Position {
       }
       enPassantTargetSquare = (startSquare - endSquare == 16) ? startSquare - 8 : null;
       if (endSquare < 8) {
-        board[endSquare] = Piece.pieceByFenCharacter[promotingPiece]!;
+        board[endSquare] = Piece.pieceByFenCharacter[promotingPiece?.toUpperCase()]!;
       }
       return;
     }
@@ -263,7 +263,7 @@ class Position {
       }
       enPassantTargetSquare = (endSquare - startSquare == 16) ? startSquare + 8 : null;
       if (endSquare > 55) {
-        board[endSquare] = Piece.pieceByFenCharacter[promotingPiece]!;
+        board[endSquare] = Piece.pieceByFenCharacter[promotingPiece?.toLowerCase()]!;
       }
       return;
     }