--- a/src/chess/fen.h	Sun Jun 07 16:56:22 2026 +0200
+++ b/src/chess/fen.h	Fri Jun 12 13:34:35 2026 +0200
@@ -37,6 +37,13 @@
 #endif
 
 /**
+ * A generous upper bound on the length of a FEN string.
+ *
+ * This includes a terminating null character.
+ */
+#define FEN_MAX_LENGTH 96
+
+/**
  * Computes the FEN representation of the current game state.
  *
  * @param str a buffer large enough to hold the FEN string