diff -r 93c81539b702 -r c0acc89d6c01 src/chess/rules.c
--- a/src/chess/rules.c	Sun Aug 23 12:19:05 2026 +0200
+++ b/src/chess/rules.c	Mon Aug 24 13:20:19 2026 +0200
@@ -645,7 +645,7 @@
 
     /* must move */
     if (move->fromfile == move->tofile && move->fromrow == move->torow) {
-        return INVALID_MOVE_SYNTAX;
+        return RULES_VIOLATED;
     }
 
     /* does piece exist */
@@ -667,7 +667,7 @@
         if (!move->capture || piece_type(move->piece) != PAWN ||
                 !enpassant_threat_exists(gamestate,
                     move->fromrow, move->tofile)) {
-            return INVALID_MOVE_SYNTAX;
+            return RULES_VIOLATED;
         }
     }