diff --git a/src/Game/Game.php b/src/Game/Game.php
index c4eaa37..d79efdc 100644
--- a/src/Game/Game.php
+++ b/src/Game/Game.php
@@ -152,7 +152,7 @@ class Game {
 
     private function getCandidateMovesForPiece(
         Piece       $piece,
-        array       $opponentPieces,
+        array       &$opponentPieces,
         FieldBitMap $occupied,
         FieldBitMap $capturableForNonPawn,
         FieldBitMap $captureableForPawn,
@@ -186,6 +186,33 @@ class Game {
         return $futureGame->getGameState(true) != GameState::ILLEGAL;
     }
 
+    private function getCastleMoves(
+        array &$ownPieces,
+        FieldBitMap $occupied,
+        FieldBitMap $capturable,
+        FieldBitMap $threatened
+    ): array {
+        $king = $this->getKing($this->current);
+        return array_values(
+            array_map(
+                fn($r) => new Move(
+                    $king,
+                    new Position(
+                        $king->getPosition()->file + 2 * ($r->getPosition()->file <=> $king->getPosition()->file),
+                        $king->getPosition()->rank,
+                    ),
+                    null,
+                    null,
+                    $r,
+                ),
+                array_filter(
+                    array_filter($ownPieces, fn($p) => $p instanceof Rook),
+                    fn($r) => $king->canCastle($occupied, $capturable, $threatened, $r)
+                )
+            )
+        );
+    }
+
     private function getLegalMovesParameterized(
         array &$ownPieces,
         array &$opponentPieces,
@@ -207,7 +234,17 @@ class Game {
             ));
         }
 
-        return array_values(array_filter($candidates, [$this, "isMoveLegal"]));
+        $candidates = array_values(array_filter($candidates, [$this, "isMoveLegal"]));
+
+        // castle moves should always be legal
+        $candidates = array_merge($candidates, $this->getCastleMoves(
+            $ownPieces,
+            $occupied,
+            $capturableNonPawn,
+            $threatened,
+        ));
+
+        return $candidates;
     }
 
     public function apply(Move $move): Game {
diff --git a/src/Game/Move.php b/src/Game/Move.php
index 0c4dd9e..2b4d39f 100644
--- a/src/Game/Move.php
+++ b/src/Game/Move.php
@@ -7,12 +7,20 @@ class Move {
     public Position $target;
     public ?Piece $captures = null;
     public ?PieceType $promoteTo = null;
+    public ?Piece $castleWith = null;
 
-    public function __construct(Piece $piece, Position $target, ?Piece $captures = null, ?PieceType $promoteTo = null) {
+    public function __construct(
+        Piece $piece,
+        Position $target,
+        ?Piece $captures = null,
+        ?PieceType $promoteTo = null,
+        ?Piece $castleWith = null,
+    ) {
         $this->piece = $piece;
         $this->target = $target;
         $this->captures = $captures;
         $this->promoteTo = $promoteTo;
+        $this->castleWith = $castleWith;
     }
 
     public function equals(Move $move): bool {
@@ -22,7 +30,11 @@ class Move {
                 ($this->captures != null && $move->captures != null && $this->captures->equals($move->captures)) ||
                 ($this->captures == null && $move->captures == null)
             ) &&
-            $this->promoteTo == $move->promoteTo;
+            $this->promoteTo == $move->promoteTo &&
+            (
+                ($this->castleWith != null && $move->castleWith != null && $this->castleWith->equals($move->castleWith)) ||
+                ($this->castleWith == null && $move->castleWith == null)
+            );
     }
 
     public function __toString(): string {
diff --git a/tests/Game/GameTest.php b/tests/Game/GameTest.php
index 7ec259f..b5b3b67 100644
--- a/tests/Game/GameTest.php
+++ b/tests/Game/GameTest.php
@@ -400,4 +400,52 @@ final class GameTest extends TestCase {
             new Pawn(new Position(5, 3), Side::WHITE),
         ), $legalMoves);
     }
+
+    public function testLegalMoves_castle() {
+        $subject = new Game(
+            [
+                new King(new Position(0, 7), Side::BLACK),
+                new King(new Position(4, 0), Side::WHITE),
+                new Queen(new Position(2, 1), Side::BLACK),
+                new Rook(new Position(7, 0), Side::WHITE),
+                new Rook(new Position(7, 1), Side::BLACK),
+            ],
+            Side::WHITE
+        );
+
+        $legalMoves = $subject->getLegalMoves();
+
+        echo join("\n", $legalMoves);
+
+        $this->assertCount(5, $legalMoves);
+
+        $this->assertContainsEqualsOnce(new Move(
+            new King(new Position(4, 0), Side::BLACK),
+            new Position(5, 0),
+        ), $legalMoves);
+
+        $this->assertContainsEqualsOnce(new Move(
+            new King(new Position(4, 0), Side::BLACK),
+            new Position(6, 0),
+            null,
+            null,
+            new Rook(new Position(7, 0), Side::WHITE),
+        ), $legalMoves);
+
+        $this->assertContainsEqualsOnce(new Move(
+            new Rook(new Position(7, 0), Side::WHITE),
+            new Position(6, 0),
+        ), $legalMoves);
+
+        $this->assertContainsEqualsOnce(new Move(
+            new Rook(new Position(7, 0), Side::WHITE),
+            new Position(5, 0),
+        ), $legalMoves);
+
+        $this->assertContainsEqualsOnce(new Move(
+            new Rook(new Position(7, 0), Side::WHITE),
+            new Position(7, 1),
+            new Rook(new Position(7, 1), Side::BLACK),
+        ), $legalMoves);
+    }
 }
\ No newline at end of file