diff --git a/sys/net/if_spppsubr.c b/sys/net/if_spppsubr.c
index 0853e5575b63..84d8843c49bf 100644
--- a/sys/net/if_spppsubr.c
+++ b/sys/net/if_spppsubr.c
@@ -281,7 +281,7 @@ static struct callout_handle keepalive_ch;
  *
  * XXX is this really still necessary?  - joerg -
  */
-static u_short interactive_ports[8] = {
+static const u_short interactive_ports[8] = {
 	0,	513,	0,	0,
 	0,	21,	0,	23,
 };