diff --git a/src/position.cpp b/src/position.cpp
index 982352c5..2d511938 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -226,7 +226,7 @@ void Position::set(const string& fenStr, bool isChess960, Thread* th) {
       incremented after Black's move.
 */
 
-  char col, row, token;
+  unsigned char col, row, token;
   size_t idx;
   Square sq = SQ_A8;
   std::istringstream ss(fenStr);