diff --git a/docs/modeltranslation/registration.rst b/docs/modeltranslation/registration.rst
index a0dd9a8..7db585b 100644
--- a/docs/modeltranslation/registration.rst
+++ b/docs/modeltranslation/registration.rst
@@ -192,6 +192,8 @@ can use the ``update_translation_fields`` command below. See
 Required fields
 ---------------
 
+.. versionadded:: 0.8
+
 By default, all translation fields are optional (not required). It can be changed using special
 attribute on ``TranslationOptions``, though::
 
diff --git a/modeltranslation/translator.py b/modeltranslation/translator.py
index e348840..bc9393c 100644
--- a/modeltranslation/translator.py
+++ b/modeltranslation/translator.py
@@ -88,7 +88,7 @@ class TranslationOptions(with_metaclass(FieldsAggregationMetaClass, object)):
                             'Fieldname in required_languages which is not in fields option.')
 
     def _check_languages(self, languages, extra=()):
-        correct = mt_settings.AVAILABLE_LANGUAGES + list(extra)
+        correct = list(mt_settings.AVAILABLE_LANGUAGES) + list(extra)
         if any(l not in correct for l in languages):
             raise ImproperlyConfigured(
                 'Language in required_languages which is not in AVAILABLE_LANGUAGES.')