--- contrib/python/moto/py3/moto/s3/responses.py	(index)
+++ contrib/python/moto/py3/moto/s3/responses.py	(working tree)
@@ -2000,7 +2000,8 @@ class S3Response(BaseResponse):
             tagging = self._tagging_from_headers(request.headers)
             storage_type = request.headers.get("x-amz-storage-class", "STANDARD")
             acl = self._acl_from_headers(request.headers)
-
+            if acl is None:
+                acl = self.backend.get_bucket(bucket_name).acl
             multipart_id = self.backend.create_multipart_upload(
                 bucket_name,
                 key_name,