diff --git a/lib/redmine/codeset_util.rb b/lib/redmine/codeset_util.rb
index bb1f972..bd4803b 100644
--- a/lib/redmine/codeset_util.rb
+++ b/lib/redmine/codeset_util.rb
@@ -25,11 +25,7 @@ module Redmine
         str = str.encode("UTF-8", :invalid => :replace,
               :undef => :replace, :replace => '?')
       else
-        str.force_encoding("UTF-8")
-        if ! str.valid_encoding?
-          str = str.encode("US-ASCII", :invalid => :replace,
-                :undef => :replace, :replace => '?').encode("UTF-8")
-        end
+        str = replace_invalid_utf8(str)
       end
       str
     end