diff --git a/app/mailers/user_mailer.rb b/app/mailers/user_mailer.rb
index 11340375c4..60d1b21508 100644
--- a/app/mailers/user_mailer.rb
+++ b/app/mailers/user_mailer.rb
@@ -445,6 +445,7 @@ class DueIssuesReminder
 
     issues_by_assignee = WorkPackage.includes(:status, :assigned_to, :project, :type)
                          .where(s.conditions)
+                         .references(:projects)
                          .group_by(&:assigned_to)
     issues_by_assignee.each do |assignee, issues|
       UserMailer.reminder_mail(assignee, issues, @days).deliver if assignee && assignee.active?