diff --git a/src/ChessArbiter.cpp b/src/ChessArbiter.cpp
index 0064234..9207e80 100644
--- a/src/ChessArbiter.cpp
+++ b/src/ChessArbiter.cpp
@@ -7,7 +7,7 @@ ChessArbiter::ChessArbiter()
   Setup("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
 }
 
-void ChessArbiter::Setup(std::string fen) {
+void ChessArbiter::Setup(const std::string fen) {
   positions.clear();
   SetFEN(fen);
   positions[this->fen.board] = 1;
@@ -39,7 +39,7 @@ bool ChessArbiter::IsCheck(bool isBlack) {
   return (IsAttacked(kingloc, !isBlack));
 }
 
-bool ChessArbiter::Play(std::string move, char promote) {
+bool ChessArbiter::Play(const std::string move, const char promote) {
   std::vector<std::string> moves = ListLegalMoves(fen.player);
   if (find(moves.begin(), moves.end(), move) != moves.end()) {
     Piece moved = board.GetPieceAt(move.substr(0, 2)); // This call never fail
@@ -189,7 +189,7 @@ bool ChessArbiter::Play(std::string move, char promote) {
 
 bool ChessArbiter::WasEnPassant() { return (was_enpassant); }
 
-bool ChessArbiter::IsAttacked(std::string square, bool by) {
+bool ChessArbiter::IsAttacked(const std::string square, const bool by) {
   std::vector<std::string> moves = board.ListPossibleMoves(by);
   for (std::string &m : moves) {
     std::string src = m.substr(0, 2);
@@ -209,7 +209,7 @@ bool ChessArbiter::IsAttacked(std::string square, bool by) {
   return (false);
 }
 
-bool ChessArbiter::IsCastlePossible(bool isBlack, bool isLong) {
+bool ChessArbiter::IsCastlePossible(const bool isBlack, const bool isLong) {
 
   if (isBlack && isLong && fen.black_castle_long) {
     if (board.IsEmpty("d8") && board.IsEmpty("c8") && board.IsEmpty("b8")) {
@@ -273,7 +273,7 @@ int ChessArbiter::GetMaterialScore() {
   return (whiteScore - blackScore);
 }
 
-std::string ChessArbiter::GetCaptures(bool isBlack) {
+std::string ChessArbiter::GetCaptures(const bool isBlack) {
   std::string captures;
   // Pawn
   char p = 'P';
@@ -320,7 +320,7 @@ std::string ChessArbiter::GetCaptures(bool isBlack) {
   return (captures);
 }
 
-std::vector<std::string> ChessArbiter::ListLegalMoves(bool isBlack) {
+std::vector<std::string> ChessArbiter::ListLegalMoves(const bool isBlack) {
   std::vector<std::string> moves;
   for (std::string &move : board.ListPossibleMoves(isBlack)) {
     std::string src = move.substr(0, 2);
@@ -425,7 +425,7 @@ bool ChessArbiter::IsCheckMate() {
 std::string ChessArbiter::GetSAN() { return (SAN); }
 char ChessArbiter::GetCapture() { return (capture); }
 
-std::string ChessArbiter::ParseSAN(std::string SANMove) {
+std::string ChessArbiter::ParseSAN(const std::string SANMove) {
   std::string src, dst;
   char piece = ' ';
   char hint = ' ';
@@ -530,15 +530,11 @@ std::string ChessArbiter::ParseSAN(std::string SANMove) {
   return (src + dst);
 }
 
-char ChessArbiter::ParseSANPromotion(std::string SANMove){
-  for(short i=0;i<SANMove.length();i++){
-    if(SANMove[i]=='='){
-      if((i+1)<SANMove.length()){
-        char p=SANMove[i+1]; // Must be upper
-        if(p=='Q' || p=='R' || p=='B' || p=='N'){
-          return SANMove[i+1];
-        }
-      }
+char ChessArbiter::ParseSANPromotion(const std::string SANMove){
+  if(SANMove.length()>=4 && SANMove[0] - 'a' < 8 && SANMove[2]=='='){
+    char p=SANMove[3]; // Must be upper
+    if(p=='Q' || p=='R' || p=='B' || p=='N'){
+      return p;
     }
   }
   return 'Q';
diff --git a/src/ChessArbiter.hpp b/src/ChessArbiter.hpp
index d63ab06..1379db2 100644
--- a/src/ChessArbiter.hpp
+++ b/src/ChessArbiter.hpp
@@ -37,16 +37,16 @@ class ChessArbiter {
 
 public:
   ChessArbiter();
-  void Setup(std::string);
+  void Setup(const std::string);
   std::string GetFEN();
   /// @brief Check which player is going to play
   bool IsBlackTurn();
   /// @brief Check if a side is in check
   bool IsCheck(bool);
   /// @brief Play a move (return false if it's illegal)
-  bool Play(std::string, char promote='Q');
+  bool Play(const std::string, const char promote='Q');
   /// @brief Check if a square is attacked by a particular player
-  bool IsAttacked(std::string, bool);
+  bool IsAttacked(const std::string, const bool);
   /// @brief Get the serialized board
   std::string GetBoard();
   /// @brief Get current position evaluation according to player's material
@@ -54,14 +54,14 @@ public:
   /// @brief Check if position is legal to be played
   bool IsPlayable();
   /// @brief Get pieces captures by a player
-  std::string GetCaptures(bool);
+  std::string GetCaptures(const bool);
   char GetCapture();
   /// @brief Get the english SAN format of the last move
   std::string GetSAN();
   /// @brief List all the legal moves of a player
-  std::vector<std::string> ListLegalMoves(bool);
+  std::vector<std::string> ListLegalMoves(const bool);
   /// @brief Check if a specific castle is possible by a player
-  bool IsCastlePossible(bool, bool);
+  bool IsCastlePossible(const bool, const bool);
   bool IsCheckMate();
   /// @brief Draws check
   bool IsDrawByFiftyMoveRule();
@@ -69,7 +69,7 @@ public:
   bool IsDrawByRepetitions();
   bool IsDraw();
   bool WasEnPassant();
-  std::string ParseSAN(std::string SANMove);
-  char ParseSANPromotion(std::string SANMove);
+  std::string ParseSAN(const std::string SANMove);
+  char ParseSANPromotion(const std::string SANMove);
 };
 } // namespace chessarbiter