diff --git a/lib/attachments_controller_patch.rb b/lib/attachments_controller_patch.rb
index 38ef80f..f5240be 100644
--- a/lib/attachments_controller_patch.rb
+++ b/lib/attachments_controller_patch.rb
@@ -9,7 +9,7 @@ module AttachmentsControllerPatch
               @diff_type = params[:type] || User.current.pref[:diff_type] || 'inline'
               @diff_type = 'inline' unless %w(inline sbs).include?(@diff_type)
               if (@diff.start_with?("From"))
-                @diff_format_patch = @diff.match(/(Subject.*)^---$/m)[0].sub(/^---$/m, '');
+                @diff_format_patch = @diff.match(/(Subject.*)^---$/m)[0].sub(/^---$/m, '').force_encoding('UTF-8');
               else
                 @diff_format_patch = nil;
               end