diff --git a/app/controllers/messages_controller.rb b/app/controllers/messages_controller.rb
index 993018a..92b85d6 100644
--- a/app/controllers/messages_controller.rb
+++ b/app/controllers/messages_controller.rb
@@ -3,6 +3,7 @@ class MessagesController < ApplicationController
 
   # GET /ruby-dev
   def index(list_name: nil, yyyymm: nil, q: nil)
+    yyyymm = yyyymm.to_i
     if list_name
       @list = List.find_by_name list_name
 
diff --git a/app/views/shared/_yyyymm_selector.html.erb b/app/views/shared/_yyyymm_selector.html.erb
index f98d391..f5739b4 100644
--- a/app/views/shared/_yyyymm_selector.html.erb
+++ b/app/views/shared/_yyyymm_selector.html.erb
@@ -1,24 +1,23 @@
 <%
-  selected_year = @yyyymm&.[](0, 4)
-  selected_month = @yyyymm&.[](4, 2)
-  years_with_months = @yyyymms.group_by {|yyyymm| yyyymm[0, 4] }.sort.reverse
+  selected_year, selected_month = @yyyymm&.divmod 100
+  years_with_months = @yyyymms.group_by {|yyyymm| yyyymm / 100 }.sort.reverse
 %>
 
 <div class="mt-6 border border-gray-200 dark:border-gray-700 rounded-lg p-3 bg-white dark:bg-gray-800">
   <!-- Year tabs -->
   <div class="flex gap-2 overflow-x-auto pb-2 mb-3 border-b border-gray-200 dark:border-gray-700">
     <% years_with_months.each do |year, months| %>
-      <%= link_to year, [@list, yyyymm: "#{year}#{months.sort.first[4, 2]}"], class: "px-3 py-1 text-sm font-medium rounded whitespace-nowrap transition-colors #{selected_year == year ? 'bg-red-600 dark:bg-red-500 text-white' : 'bg-gray-100 dark:bg-gray-900 text-gray-600 dark:text-gray-400 hover:text-gray-900 dark:hover:text-gray-100'}" %>
+      <%= link_to year, [@list, yyyymm: "#{year}#{'%02d' % months.sort.first.modulo(100)}"], class: "px-3 py-1 text-sm font-medium rounded whitespace-nowrap transition-colors #{selected_year == year ? 'bg-red-600 dark:bg-red-500 text-white' : 'bg-gray-100 dark:bg-gray-900 text-gray-600 dark:text-gray-400 hover:text-gray-900 dark:hover:text-gray-100'}" %>
     <% end %>
   </div>
 
   <!-- Month tabs -->
   <% if selected_year %>
     <div class="flex gap-1 flex-wrap">
-      <% available_months = years_with_months.detect {|y, _| y == selected_year }&.last&.map {|yyyymm| yyyymm[4, 2] } || [] %>
-      <% ('01'..'12').each do |month| %>
+      <% available_months = years_with_months.detect {|y, _| y == selected_year }&.last&.map {|yyyymm| yyyymm.modulo 100 } || [] %>
+      <% (1..12).each do |month| %>
         <% if available_months.include?(month) %>
-          <%= link_to month, [@list, yyyymm: "#{selected_year}#{month}"], class: "px-2 py-1 text-xs font-medium rounded transition-colors #{selected_month == month ? 'bg-red-600 dark:bg-red-500 text-white border-2 border-red-700 dark:border-red-400' : 'bg-gray-100 dark:bg-gray-900 text-gray-600 dark:text-gray-400 hover:text-gray-900 dark:hover:text-gray-100 border-2 border-transparent'}" %>
+          <%= link_to month, [@list, yyyymm: "#{selected_year}#{'%02d' % month}"], class: "px-2 py-1 text-xs font-medium rounded transition-colors #{selected_month == month ? 'bg-red-600 dark:bg-red-500 text-white border-2 border-red-700 dark:border-red-400' : 'bg-gray-100 dark:bg-gray-900 text-gray-600 dark:text-gray-400 hover:text-gray-900 dark:hover:text-gray-100 border-2 border-transparent'}" %>
         <% else %>
           <span class="px-2 py-1 text-xs font-medium rounded text-gray-300 dark:text-gray-600 border-2 border-transparent"><%= month %></span>
         <% end %>