diff --git a/django/utils/formats.py b/django/utils/formats.py
index c23a37cb2b..1eb7a3d837 100644
--- a/django/utils/formats.py
+++ b/django/utils/formats.py
@@ -24,7 +24,9 @@ def iter_format_modules(lang):
             format_locations.append(settings.FORMAT_MODULE_PATH + '.%s')
             format_locations.reverse()
         locale = to_locale(lang)
-        locales = set((locale, locale.split('_')[0]))
+        locales = [locale]
+        if '_' in locale:
+            locales.append(locale.split('_')[0])
         for location in format_locations:
             for loc in locales:
                 try:
diff --git a/tests/regressiontests/i18n/tests.py b/tests/regressiontests/i18n/tests.py
index 0a6f621e3c..98c0ed9aaa 100644
--- a/tests/regressiontests/i18n/tests.py
+++ b/tests/regressiontests/i18n/tests.py
@@ -480,6 +480,19 @@ class FormattingTests(TestCase):
             settings.FORMAT_MODULE_PATH = old_format_module_path
             deactivate()
 
+    def test_iter_format_modules_stability(self):
+        """
+        Tests the iter_format_modules function always yields format modules in
+        a stable and correct order in presence of both base ll and ll_CC formats.
+        """
+        try:
+            old_l10n, settings.USE_L10N = settings.USE_L10N, True
+            en_format_mod = import_module('django.conf.locale.en.formats')
+            en_gb_format_mod = import_module('django.conf.locale.en_GB.formats')
+            self.assertEqual(list(iter_format_modules('en-gb')), [en_gb_format_mod, en_format_mod])
+        finally:
+            settings.USE_L10N = old_l10n
+
     def test_localize_templatetag_and_filter(self):
         """
         Tests the {% localize %} templatetag