diff --git a/zerver/migrations/0021_migrate_attachment_data.py b/zerver/migrations/0021_migrate_attachment_data.py
index 6757ae0fa9..a0df138637 100644
--- a/zerver/migrations/0021_migrate_attachment_data.py
+++ b/zerver/migrations/0021_migrate_attachment_data.py
@@ -20,7 +20,7 @@ def migrate_existing_data(apps, schema_editor):
             if owner == message.sender:
                 if message.recipient.type == Recipient.STREAM:
                     stream = Stream.objects.get(id=message.recipient.type_id)
-                    is_realm_public = stream.realm.domain != "mit.edu" and not stream.invite_only
+                    is_realm_public = not stream.realm.is_zephyr_mirror_realm and not stream.invite_only
                     entry.is_realm_public = entry.is_realm_public or is_realm_public
 
         entry.save()
diff --git a/zerver/migrations/0041_create_attachments_for_old_messages.py b/zerver/migrations/0041_create_attachments_for_old_messages.py
index fe7fb00628..e7a9ff812f 100644
--- a/zerver/migrations/0041_create_attachments_for_old_messages.py
+++ b/zerver/migrations/0041_create_attachments_for_old_messages.py
@@ -25,7 +25,7 @@ def check_and_create_attachments(apps, schema_editor):
             is_message_realm_public = False
             if message.recipient.type == STREAM:
                 stream = Stream.objects.get(id=message.recipient.type_id)
-                is_message_realm_public = not stream.invite_only and stream.realm.domain != "mit.edu"
+                is_message_realm_public = not stream.invite_only and not stream.realm.is_zephyr_mirror_realm
 
             if path_id is not None:
                 attachment = Attachment.objects.create(