diff --git a/app/controllers/personal_books_controller.rb b/app/controllers/personal_books_controller.rb
index 8b83b5c..afcb43a 100644
--- a/app/controllers/personal_books_controller.rb
+++ b/app/controllers/personal_books_controller.rb
@@ -32,7 +32,7 @@ class PersonalBooksController < ApplicationController
          books_show = books_temp.select {|value| value.create_link.include? params[:keywords]}
         end
       when "publish_date", "publication_date"
-          books_show = books_temp.select {|value| value.publication_date.strftime("%Y/%m").include? params[:keywords]}
+          books_show = books_temp.select {|value| value.publication_date.strftime("%Y/%m").to_s.include? params[:keywords]}
       when "author_type"
           books_show = books_temp.select {|value| value.book_author_types.collect{|bat| bat.title}.join(", ").include? params[:keywords]}
       when "language"