Index: head/contrib/blacklist/libexec/blacklistd-helper
===================================================================
--- head/contrib/blacklist/libexec/blacklistd-helper
+++ head/contrib/blacklist/libexec/blacklistd-helper
@@ -63,8 +63,11 @@
 		tname="port$6"
 		/sbin/ipfw table $tname create type addr 2>/dev/null
 		/sbin/ipfw -q table $tname add "$addr/$mask"
-		/sbin/ipfw -q add $rule drop $3 from "table("$tname")" to \
-		    any dst-port $6 && echo OK
+		# if rule number $rule does not already exist, create it
+		/sbin/ipfw show $rule >/dev/null 2>&1 || \
+			/sbin/ipfw add $rule drop $3 from \
+			table"("$tname")" to any dst-port $6 >/dev/null && \
+			echo OK
 		;;
 	npf)
 		/sbin/npfctl rule "$2" add block in final $proto from \