diff --git a/outpostcli/lfs/storage_class/s3.py b/outpostcli/lfs/storage_class/s3.py
index f774cc6..7385636 100644
--- a/outpostcli/lfs/storage_class/s3.py
+++ b/outpostcli/lfs/storage_class/s3.py
@@ -61,38 +61,61 @@ def s3_multipart_upload(msg: Dict[str, Any]):
     _log.info({"cores": cores})
     bytes_so_far = 0
     try:
-        with multimap(cores) as pmap:
-            for resp in pmap(
-                transfer_part,
-                (
-                    PartInfo(
-                        filepath,
-                        part_no,
-                        chunk_size,
-                        signed_url,
-                    )
-                    for (part_no, signed_url) in pre_signed_urls
-                ),
-            ):
-                if isinstance(resp, ProxyLFSException):
-                    raise LFSException(
-                        code=resp.code,
-                        message=resp.message,
-                        doc_url=resp.doc_url,
-                    )
-                else:
-                    bytes_so_far += chunk_size
-                    # Not precise but that's ok.
-                    write_msg(
-                        {
-                            "event": "progress",
-                            "oid": oid,
-                            "bytesSoFar": bytes_so_far,
-                            "bytesSinceLast": chunk_size,
-                        }
-                    )
-                    parts.append(resp)
-                pass
+        for part_no, signed_url in pre_signed_urls:
+            part_info = PartInfo(filepath, part_no, chunk_size, signed_url)
+            resp = transfer_part(part_info)
+            if isinstance(resp, ProxyLFSException):
+                raise LFSException(
+                    code=resp.code,
+                    message=resp.message,
+                    doc_url=resp.doc_url,
+                )
+            else:
+                bytes_so_far += chunk_size
+                # Not precise but that's ok.
+                write_msg(
+                    {
+                        "event": "progress",
+                        "oid": oid,
+                        "bytesSoFar": bytes_so_far,
+                        "bytesSinceLast": chunk_size,
+                    }
+                )
+                parts.append(resp)
+            pass
+
+        # with multimap(cores) as pmap:
+        #     for resp in pmap(
+        #         transfer_part,
+        #         (
+        #             PartInfo(
+        #                 filepath,
+        #                 part_no,
+        #                 chunk_size,
+        #                 signed_url,
+        #             )
+        #             for (part_no, signed_url) in pre_signed_urls
+        #         ),
+        #     ):
+        #         if isinstance(resp, ProxyLFSException):
+        #             raise LFSException(
+        #                 code=resp.code,
+        #                 message=resp.message,
+        #                 doc_url=resp.doc_url,
+        #             )
+        #         else:
+        #             bytes_so_far += chunk_size
+        #             # Not precise but that's ok.
+        #             write_msg(
+        #                 {
+        #                     "event": "progress",
+        #                     "oid": oid,
+        #                     "bytesSoFar": bytes_so_far,
+        #                     "bytesSinceLast": chunk_size,
+        #                 }
+        #             )
+        #             parts.append(resp)
+        #         pass
         complete_resp = complete_multipart_upload(complete_url, parts)
         if isinstance(complete_resp, LFSException):
             abort_resp = abort_multipart_upload(abort_url)