diff --git a/IPython/nbformat/v2/nbjson.py b/IPython/nbformat/v2/nbjson.py
index b86297d..e67bec3 100644
--- a/IPython/nbformat/v2/nbjson.py
+++ b/IPython/nbformat/v2/nbjson.py
@@ -48,6 +48,7 @@ class JSONWriter(NotebookWriter):
     def writes(self, nb, **kwargs):
         kwargs['cls'] = BytesEncoder
         kwargs['indent'] = 4
+        kwargs['sort_keys'] = True
         return json.dumps(nb, **kwargs)