diff --git a/OOP_2B6_PROJECT/src/backend/Board.java b/OOP_2B6_PROJECT/src/backend/Board.java
index 0ebe564..7c4c66f 100644
--- a/OOP_2B6_PROJECT/src/backend/Board.java
+++ b/OOP_2B6_PROJECT/src/backend/Board.java
@@ -89,6 +89,7 @@ public class Board {
         if (gameOver) return;
 
         Piece clickedPiece = getPieceAt(x, y);
+
         if (selectedX == null || selectedY == null) {
             if (clickedPiece != null && clickedPiece.isWhite() == turnIsWhite) {
                 selectedX = x;
@@ -98,31 +99,50 @@ public class Board {
         } else {
             Piece selectedPiece = getPieceAt(selectedX, selectedY);
             if (selectedPiece != null && selectedPiece.isWhite() == turnIsWhite) {
-                Piece captured = getPieceAt(x, y);
-                pieces.removeIf(p -> p.getX() == x && p.getY() == y);
-                pieces.removeIf(p -> p.getX() == selectedX && p.getY() == selectedY);
-                Piece moved = new Piece(
+
+                // simulate move
+                Board simulation = new Board(this);
+                simulation.pieces.removeIf(p -> p.getX() == selectedX && p.getY() == selectedY);
+                simulation.pieces.removeIf(p -> p.getX() == x && p.getY() == y);
+                simulation.pieces.add(new Piece(
                     selectedPiece.isWhite(),
                     selectedPiece.getType(),
                     x,
                     y
-                );
-                pieces.add(moved);
-                Move move = new Move(selectedPiece, selectedX, selectedY, x, y, captured);
-                moveHistory.push(move);
-                turnNumber++;
-                turnIsWhite = !turnIsWhite;
+                ));
 
-                if (isCheckmate(!turnIsWhite)) {
-                    gameOver = true;
+                // check if move is legal (king remains safe)
+                if (!simulation.isKingInCheck(turnIsWhite)) {
+                    Piece captured = getPieceAt(x, y);
+                    pieces.removeIf(p -> p.getX() == x && p.getY() == y);
+                    pieces.removeIf(p -> p.getX() == selectedX && p.getY() == selectedY);
+                    pieces.add(new Piece(
+                        selectedPiece.isWhite(),
+                        selectedPiece.getType(),
+                        x,
+                        y
+                    ));
+
+                    Move move = new Move(selectedPiece, selectedX, selectedY, x, y, captured);
+                    moveHistory.push(move);
+                    turnNumber++;
+                    turnIsWhite = !turnIsWhite;
+
+                    // check for checkmate on the opponent
+                    if (isCheckmate(!turnIsWhite)) {
+                        gameOver = true;
+                    }
                 }
             }
+
+            // deselect in all cases
             selectedX = null;
             selectedY = null;
             highlightedPositions.clear();
         }
     }
 
+
     public void undoLastMove() {
         if (!moveHistory.isEmpty()) {
             Move lastMove = moveHistory.pop();