https://bugs.gentoo.org/707456
--- a/src/wepfilter.c
+++ b/src/wepfilter.c
@@ -30,7 +30,7 @@
 #include "config.h"
 #include "misc.h"
 
-int server_mode;
+extern int server_mode;
 static int capture_successfull = 0;
 static wlan_packet_list* head = NULL;