diff --git a/traitlets/traitlets.py b/traitlets/traitlets.py
index 01048c3c..3fa098ea 100644
--- a/traitlets/traitlets.py
+++ b/traitlets/traitlets.py
@@ -1164,6 +1164,9 @@ def compress(past_changes, change):
                     return past_changes
 
             def hold(change):
+                if not isinstance(change, Bunch):
+                # cast to bunch if given a dict
+                    change = Bunch(change)
                 name = change.name
                 cache[name] = compress(cache.get(name), change)