diff --git a/usr.sbin/config/lang.l b/usr.sbin/config/lang.l
--- a/usr.sbin/config/lang.l
+++ b/usr.sbin/config/lang.l
@@ -90,7 +90,7 @@
 int kw_lookup(char *);
 unsigned int octal(const char *);
 unsigned int hex(const char *);
-int yyerror(const char *);
+void yyerror(const char *);
 
 #define YY_DECL int yylex(void)
 %}