diff --git a/common/test/acceptance/fixtures/base.py b/common/test/acceptance/fixtures/base.py
index a327a3157c..652ae43573 100644
--- a/common/test/acceptance/fixtures/base.py
+++ b/common/test/acceptance/fixtures/base.py
@@ -166,10 +166,7 @@ class XBlockContainerFixture(StudioApiFixture):
         """
         Encode `post_dict` (a dictionary) as UTF-8 encoded JSON.
         """
-        return json.dumps({
-            k: v.encode('utf-8') if isinstance(v, six.string_types) else v
-            for k, v in post_dict.items()
-        })
+        return json.dumps(post_dict).encode('utf-8')
 
     def get_nested_xblocks(self, category=None):
         """