diff --git a/app/models/card/exportable.rb b/app/models/card/exportable.rb
index ffff82581..b147c47d9 100644
--- a/app/models/card/exportable.rb
+++ b/app/models/card/exportable.rb
@@ -67,7 +67,7 @@ module Card::Exportable
     end
 
     def collect_attachments
-      attachments.to_a + comments.flat_map { |c| c.attachments.to_a }
+      (attachments.to_a + comments.flat_map { |c| c.attachments.to_a }).uniq(&:blob_id)
     end
 
     def export_status
diff --git a/app/models/zip_file.rb b/app/models/zip_file.rb
index d6fb0ad0a..f0ecf8dea 100644
--- a/app/models/zip_file.rb
+++ b/app/models/zip_file.rb
@@ -44,7 +44,12 @@ class ZipFile
         # ActiveStorage's upload method expects a read-based IO, but ZipKit
         # needs a write-based stream. The TransferManager's upload_stream
         # yields a writable IO that we can stream directly to.
-        service.send(:upload_stream, key: blob.key, part_size: 100.megabytes) do |write_stream|
+        service.send(:upload_stream,
+          key: blob.key,
+          content_type: "application/zip",
+          part_size: 100.megabytes,
+          **service.upload_options
+        ) do |write_stream|
           write_stream.binmode
           writer.stream_to(write_stream)
           yield writer