https://narkive.com/5o9wtufe.5

--- a/sendmail/conf.c
+++ b/sendmail/conf.c
@@ -4075,7 +4075,7 @@
 #if TCPWRAPPERS
 	char *host;
 	char *addr;
-	extern int hosts_ctl();
+	extern int hosts_ctl __P((char *, char *, char *, char*));
 #endif /* TCPWRAPPERS */
 
 	if (tTd(48, 3))