diff --git a/app/models/mailer.rb b/app/models/mailer.rb
index 6f68918a9..3aef68871 100644
--- a/app/models/mailer.rb
+++ b/app/models/mailer.rb
@@ -354,7 +354,7 @@ class Mailer < ActionMailer::Base
                                           :conditions => s.conditions
                                     ).group_by(&:assigned_to)
     issues_by_assignee.each do |assignee, issues|
-      deliver_reminder(assignee, issues, days) if assignee && assignee.active?
+      deliver_reminder(assignee, issues, days) if assignee.is_a?(User) && assignee.active?
     end
   end