diff --git a/config/filter.d/proftpd.conf b/config/filter.d/proftpd.conf
index bf8f9b5f..ac714cc1 100644
--- a/config/filter.d/proftpd.conf
+++ b/config/filter.d/proftpd.conf
@@ -1,5 +1,7 @@
 # Fail2Ban fitler for the Proftpd FTP daemon
 #
+# Set "UseReverseDNS off" in proftpd.conf to avoid the need for DNS.
+# See: http://www.proftpd.org/docs/howto/DNS.html
 
 [INCLUDES]