diff --git a/src/misc.h b/src/misc.h
index 58646aaf..29d35d5b 100644
--- a/src/misc.h
+++ b/src/misc.h
@@ -38,7 +38,7 @@ extern void dbg_mean_of(int v);
 extern void dbg_print();
 
 class Position;
-extern Move move_from_uci(const Position& pos, std::string str);
+extern Move move_from_uci(const Position& pos, std::string& str);
 extern const std::string move_to_uci(Move m, bool chess960);
 extern const std::string move_to_san(Position& pos, Move m);
 
diff --git a/src/move.cpp b/src/move.cpp
index 62ec7579..74271b31 100644
--- a/src/move.cpp
+++ b/src/move.cpp
@@ -17,7 +17,6 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <algorithm>
 #include <cassert>
 #include <string>
 
@@ -57,10 +56,10 @@ const string move_to_uci(Move m, bool chess960) {
 /// simple coordinate notation and returns an equivalent Move if any.
 /// Moves are guaranteed to be legal.
 
-Move move_from_uci(const Position& pos, string str) {
+Move move_from_uci(const Position& pos, string& str) {
 
-  // Some GUIs, like Junior, could send promotion in uppercase
-  std::transform(str.begin(), str.end(), str.begin(), tolower);
+  if (str.length() == 5) // Junior could send promotion in uppercase
+      str[4] = char(tolower(str[4]));
 
   for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
       if (str == move_to_uci(ml.move(), pos.is_chess960()))