diff --git a/common/djangoapps/dark_lang/middleware.py b/common/djangoapps/dark_lang/middleware.py
index 88783328be..28a12e9da5 100644
--- a/common/djangoapps/dark_lang/middleware.py
+++ b/common/djangoapps/dark_lang/middleware.py
@@ -45,7 +45,7 @@ class DarkLangMiddleware(object):
         """
         ``True`` iff one of the values in ``self.released_langs`` is a prefix of ``lang_code``.
         """
-        return any(lang_code.startswith(released_lang) for released_lang in self.released_langs)
+        return any(lang_code.lower().startswith(released_lang.lower()) for released_lang in self.released_langs)
 
     def _format_accept_value(self, lang, priority=1.0):
         """
diff --git a/common/djangoapps/dark_lang/tests.py b/common/djangoapps/dark_lang/tests.py
index a445b938f0..9896851984 100644
--- a/common/djangoapps/dark_lang/tests.py
+++ b/common/djangoapps/dark_lang/tests.py
@@ -1,8 +1,6 @@
 """
 Tests of DarkLangMiddleware
 """
-from unittest import expectedFailure
-
 from django.contrib.auth.models import User
 from django.http import HttpRequest
 
@@ -123,7 +121,6 @@ class DarkLangMiddlewareTests(TestCase):
             self.process_request(accept='rel-ter;q=1.0, rel;q=0.5')
         )
 
-    @expectedFailure
     def test_accept_mixed_case(self):
         self.assertAcceptEquals(
             'rel-TER;q=1.0, REL;q=0.5',