diff --git a/usr.sbin/config/config.y b/usr.sbin/config/config.y
--- a/usr.sbin/config/config.y
+++ b/usr.sbin/config/config.y
@@ -88,7 +88,7 @@
 
 #define ns(s)	strdup(s)
 int include(const char *, int);
-void yyerror(const char *s);
+int yyerror(const char *s);
 int yywrap(void);
 
 static void newdev(char *name);
@@ -299,11 +299,13 @@
 
 %%
 
-void
+int
 yyerror(const char *s)
 {
 
 	errx(1, "%s:%d: %s", yyfile, yyline + 1, s);
+	__unreachable();
+	return (0);
 }
 
 int