diff --git a/HowtoContributeABuildbot.md b/HowtoContributeABuildbot.md
index 5e18b3c..5fad881 100644
--- a/HowtoContributeABuildbot.md
+++ b/HowtoContributeABuildbot.md
@@ -2,6 +2,8 @@
 
 You'll need [git](http://git-scm.com/) and [buildbot-slave](http://trac.buildbot.net/wiki/DownloadInstall) before you can proceed.
 
+A buildslave makes TCP connections to the buildmaster, which `tahoe-lafs.org` operates.  You do not need a publicly routable IP address.
+
 ## Configuration
 Create a user account with low privileges to run buildbot.