diff --git a/common/lib/xmodule/xmodule/modulestore/__init__.py b/common/lib/xmodule/xmodule/modulestore/__init__.py
index b7307519aa..7993996fe7 100644
--- a/common/lib/xmodule/xmodule/modulestore/__init__.py
+++ b/common/lib/xmodule/xmodule/modulestore/__init__.py
@@ -637,7 +637,7 @@ class ModuleStoreAssetBase(object):
         if asset_type is None:
             # Add assets of all types to the sorted list.
             all_assets = SortedAssetList(iterable=[], key=key_func)
-            for asset_type, val in course_assets.iteritems():
+            for asset_type, val in six.iteritems(course_assets):
                 all_assets.update(val)
         else:
             # Add assets of a single type to the sorted list.