diff --git a/lib/motion/project/testflight.rb b/lib/motion/project/testflight.rb
index 0029d6d8..f28da322 100644
--- a/lib/motion/project/testflight.rb
+++ b/lib/motion/project/testflight.rb
@@ -82,7 +82,7 @@ task :testflight => :archive do
   unless prefs.team_token
     App.fail "A value for app.testflight.team_token is mandatory"
   end
-  distribution_lists = (prefs.distribution_lists.join(',') or nil)
+  distribution_lists = (prefs.distribution_lists ? prefs.distribution_lists.join(',') : nil)
   notes = ENV['notes']
   unless notes
     App.fail "Submission notes must be provided via the `notes' environment variable. Example: rake testflight notes='w00t'"