diff --git a/app/models/project.rb b/app/models/project.rb
index 71ffdc8f5..9a65bdd2e 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -472,7 +472,7 @@ class Project < ActiveRecord::Base
   # Returns the users that should be notified on project events
   def notified_users
     # TODO: User part should be extracted to User#notify_about?
-    members.select {|m| m.mail_notification? || m.user.mail_notification == 'all'}.collect {|m| m.principal}
+    members.select {|m| m.principal.present? && (m.mail_notification? || m.principal.mail_notification == 'all')}.collect {|m| m.principal}
   end
 
   # Returns an array of all custom fields enabled for project issues