diff --git a/app/controllers/personal_patents_controller.rb b/app/controllers/personal_patents_controller.rb
index 25b8cad..a1c7546 100644
--- a/app/controllers/personal_patents_controller.rb
+++ b/app/controllers/personal_patents_controller.rb
@@ -25,7 +25,7 @@ class PersonalPatentsController < ApplicationController
       when "publish_date", "application_date", "end_date"
           patents_show = patents_temp.select {|value| search_all_words((value.send(params[:selectbox]).strftime("%Y/%m/%d") rescue ""), params[:keywords])}
       when "patent_category"
-          patent_show = patents_temp.select {|value| search_all_words((value.patent_types.collect{|pt| pt.title}.join(", ") rescue ""), params[:keywords])}
+          patent_show = patents_temp.select {|value| search_all_words((value.patent_types.collect{|pt| pt.title}.join(", ").to_s rescue ""), params[:keywords])}
       when "author_type"
           patents_show = patents_temp.select {|value| search_all_words(value.patent_author_types.collect{|pt| pt.title}.join(", "), params[:keywords])}
       when "language"