diff --git a/app/controllers/admin/seminars_controller.rb b/app/controllers/admin/seminars_controller.rb
index efe247c..f9bcc7a 100644
--- a/app/controllers/admin/seminars_controller.rb
+++ b/app/controllers/admin/seminars_controller.rb
@@ -496,6 +496,9 @@ class Admin::SeminarsController < OrbitAdminController
         if preferred_session_field.seminar_submission_values.count != 0
           seminar_submission_values = preferred_session_field.seminar_submission_values.to_a
           seminar_submission_values.each do |v|
+            if v.seminar_signup_contribute.nil?
+              v.destroy
+            end
             next if v.val.to_i.to_s != v.val
             seminar_session = @seminar.seminar_sessions.where(:key=>v.val.to_i).first
             seminar_session.default_seminar_signup_ids << v.seminar_signup_contribute.seminar_signup_id.to_s