diff --git a/Board.cpp b/Board.cpp
index 59d2173..b555725 100644
--- a/Board.cpp
+++ b/Board.cpp
@@ -51,6 +51,8 @@ CastlingRights Board::castlingRights() const {
 }
 
 void Board::setEnPassantSquare(const Square::Optional &square) {
+    if (!square.has_value())
+        return;
     mEPS = square->index();
 }