diff --git a/heat/common/wsgi.py b/heat/common/wsgi.py
index 10fe6ad8a01..b1c04fdbded 100644
--- a/heat/common/wsgi.py
+++ b/heat/common/wsgi.py
@@ -426,10 +426,15 @@ def get_content_type(self, allowed_content_types):
             return content_type
 
     def best_match_language(self):
-        """Determine language for returned response."""
+        """Determines best available locale from the Accept-Language header.
+
+        :returns: the best language match or None if the 'Accept-Language'
+                  header was not available in the request.
+        """
+        if not self.accept_language:
+            return None
         all_languages = gettextutils.get_available_languages('heat')
-        return self.accept_language.best_match(all_languages,
-                                               default_match='en_US')
+        return self.accept_language.best_match(all_languages)
 
 
 def is_json_content_type(request):
diff --git a/heat/tests/test_wsgi.py b/heat/tests/test_wsgi.py
index 4db0c63180a..01d947725e8 100644
--- a/heat/tests/test_wsgi.py
+++ b/heat/tests/test_wsgi.py
@@ -80,19 +80,25 @@ def test_content_type_accept_default(self):
         self.assertEqual(result, "application/json")
 
     def test_best_match_language(self):
-        # Here we test that we are actually invoking language negotiation
-        # by webop and also that the default locale always available is en-US
+        # Test that we are actually invoking language negotiation by webop
         request = wsgi.Request.blank('/')
         accepted = 'unknown-lang'
         request.headers = {'Accept-Language': accepted}
 
         def fake_best_match(self, offers, default_match=None):
-            return default_match
+            # Best match on an unknown locale returns None
+            return None
 
         self.stubs.SmartSet(request.accept_language,
                             'best_match', fake_best_match)
 
-        self.assertEqual(request.best_match_language(), 'en_US')
+        self.assertEqual(request.best_match_language(), None)
+
+        # If Accept-Language is missing or empty, match should be None
+        request.headers = {'Accept-Language': ''}
+        self.assertEqual(request.best_match_language(), None)
+        request.headers.pop('Accept-Language')
+        self.assertEqual(request.best_match_language(), None)
 
 
 class ResourceTest(HeatTestCase):