diff --git a/app/views/common/_diff.html.erb b/app/views/common/_diff.html.erb
index 94434fe86..0d30bedd2 100644
--- a/app/views/common/_diff.html.erb
+++ b/app/views/common/_diff.html.erb
@@ -10,7 +10,7 @@
 <thead>
 <tr>
   <th colspan="4" class="filename">
-    <%= Redmine::CodesetUtil.to_utf8_by_setting(table_file.file_name) %>
+    <%= table_file.file_name %>
   </th>
 </tr>
 </thead>
@@ -24,11 +24,11 @@
 <tr>
   <th class="line-num"><%= line.nb_line_left %></th>
   <td class="line-code <%= line.type_diff_left %>">
-    <pre><%= Redmine::CodesetUtil.to_utf8_by_setting(line.html_line_left).html_safe %></pre>
+    <pre><%= line.html_line_left.html_safe %></pre>
   </td>
   <th class="line-num"><%= line.nb_line_right %></th>
   <td class="line-code <%= line.type_diff_right %>">
-    <pre><%= Redmine::CodesetUtil.to_utf8_by_setting(line.html_line_right).html_safe %></pre>
+    <pre><%= line.html_line_right.html_safe %></pre>
   </td>
 </tr>
 <% end -%>
@@ -40,7 +40,7 @@
 <thead>
   <tr>
     <th colspan="3" class="filename">
-      <%= Redmine::CodesetUtil.to_utf8_by_setting(table_file.file_name) %>
+      <%= table_file.file_name %>
     </th>
   </tr>
 </thead>
@@ -55,7 +55,7 @@
   <th class="line-num"><%= line.nb_line_left %></th>
   <th class="line-num"><%= line.nb_line_right %></th>
   <td class="line-code <%= line.type_diff %>">
-    <pre><%= Redmine::CodesetUtil.to_utf8_by_setting(line.html_line).html_safe %></pre>
+    <pre><%= line.html_line.html_safe %></pre>
   </td>
 </tr>
 <% end -%>
diff --git a/lib/redmine/unified_diff.rb b/lib/redmine/unified_diff.rb
index 9917a554f..d08ab5c01 100644
--- a/lib/redmine/unified_diff.rb
+++ b/lib/redmine/unified_diff.rb
@@ -30,15 +30,8 @@ module Redmine
       diff_table = DiffTable.new(diff_type, diff_style)
       diff.each do |line|
         line_encoding = nil
-        if line.respond_to?(:force_encoding)
-          line_encoding = line.encoding
-          # TODO: UTF-16 and Japanese CP932 which is imcompatible with ASCII
-          #       In Japan, diffrence between file path encoding
-          #       and file contents encoding is popular.
-          line.force_encoding('ASCII-8BIT')
-        end
-        unless diff_table.add_line line
-          line.force_encoding(line_encoding) if line_encoding
+        line = Redmine::CodesetUtil.to_utf8_by_setting(line)
+        unless diff_table.add_line(line)
           self << diff_table if diff_table.length > 0
           diff_table = DiffTable.new(diff_type, diff_style)
         end