diff --git a/src/position.cpp b/src/position.cpp
index cbc64609..feb185cf 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -46,7 +46,7 @@ using std::endl;
 
 static inline bool isZero(char c) { return c == '0'; }
 
-struct PieceLetters : std::map<char, Piece> {
+struct PieceLetters : public std::map<char, Piece> {
 
     PieceLetters() {