diff --git a/dependencies/gnuchess/lexpgn.h b/dependencies/gnuchess/lexpgn.h
index 91ead55..1b6ca6f 100644
--- a/dependencies/gnuchess/lexpgn.h
+++ b/dependencies/gnuchess/lexpgn.h
@@ -24,4 +24,6 @@ extern char *pgn_blackELO;
 extern char *pgn_result;
 extern char *pgn_othertags;
 
+extern int yylex (void);
+
 #endif