diff --git a/app/models/oic_session.rb b/app/models/oic_session.rb
index 75e0b52..9239a4b 100644
--- a/app/models/oic_session.rb
+++ b/app/models/oic_session.rb
@@ -3,6 +3,7 @@ class OicSession < ActiveRecord::Base
 
   before_create :randomize_state!
   before_create :randomize_nonce!
+  before_create :clean_old_oic_with_null_user
 
   def self.client_config
     Setting.plugin_redmine_openid_connect
@@ -182,6 +183,10 @@ def user
     return @user
   end
 
+  def clean_old_oic_with_null_user
+    OicSession.where("user_id is null and updated_at < ?", 7.days.ago).delete_all
+  end
+
   def authorization_url
     config = dynamic_config
     config["authorization_endpoint"] + "?" + authorization_query.to_param