1 files changed, 1 insertions, 1 deletions

diff --git a/src/mailman/rest/moderation.py b/src/mailman/rest/moderation.py
index 0bdc50688..4373067ec 100644
--- a/src/mailman/rest/moderation.py
+++ b/src/mailman/rest/moderation.py
@@ -88,7 +88,7 @@ class _HeldMessageBase(_ModerationBase):
         # resource.  Others we can drop.  Since we're mutating the dictionary,
         # we need to make a copy of the keys.  When you port this to Python 3,
         # you'll need to list()-ify the .keys() dictionary view.
-        for key in resource.keys():
+        for key in list(resource):
             if key in ('_mod_subject', '_mod_hold_date', '_mod_reason',
                        '_mod_sender', '_mod_message_id'):
                 resource[key[5:]] = resource.pop(key)