diff --git a/src/types.h b/src/types.h
index bbfd0c71..40a2baa0 100644
--- a/src/types.h
+++ b/src/types.h
@@ -392,7 +392,7 @@ inline Rank relative_rank(Color c, Square s) {
 }
 
 inline bool opposite_colors(Square s1, Square s2) {
-  int s = s1 ^ s2;
+  int s = int(s1) ^ int(s2);
   return ((s >> 3) ^ s) & 1;
 }