diff -r e57e2874fb2a -r d1420f5c5704 src/chess/rules.c
--- a/src/chess/rules.c	Mon Aug 24 16:13:51 2026 +0200
+++ b/src/chess/rules.c	Tue Aug 25 18:35:18 2026 +0200
@@ -1158,6 +1158,11 @@
                 move->check = move->checkmate = false;
                 switch (determine_check_or_checkmate(gamestate, move)) {
                     case 2: move->checkmate = true;
+#if __STDC_VERSION__ > 202310L
+                    [[fallthrough]];
+#elif __GNUC__
+                    __attribute__((fallthrough));
+#endif
                     case 1: move->check = true;
                 }
             }