https://bugs.gentoo.org/871366
--- a/eval.h
+++ b/eval.h
@@ -107,4 +107,6 @@ struct action	*eval_end(struct ruleset *, int *, int, int);
 void		 eval_clear(struct ruleset *, int *, int);
 void		 free_ruleset(struct ruleset *);
 
+int yylex(void);
+
 #endif