diff --git a/s3tests_boto3/functional/test_s3.py b/s3tests_boto3/functional/test_s3.py
index 995fe8e..99072ff 100644
--- a/s3tests_boto3/functional/test_s3.py
+++ b/s3tests_boto3/functional/test_s3.py
@@ -6720,6 +6720,8 @@ def test_multipart_upload_small():
     response = client.complete_multipart_upload(Bucket=bucket_name, Key=key1, UploadId=upload_id, MultipartUpload={'Parts': parts})
     response = client.get_object(Bucket=bucket_name, Key=key1)
     eq(response['ContentLength'], objlen)
+    # check extra client.complete_multipart_upload
+    response = client.complete_multipart_upload(Bucket=bucket_name, Key=key1, UploadId=upload_id, MultipartUpload={'Parts': parts})
 
 def _create_key_with_random_content(keyname, size=7*1024*1024, bucket_name=None, client=None):
     if bucket_name is None:
@@ -6936,6 +6938,8 @@ def test_multipart_upload():
 
     (upload_id, data, parts) = _multipart_upload(bucket_name=bucket_name, key=key, size=objlen, content_type=content_type, metadata=metadata)
     client.complete_multipart_upload(Bucket=bucket_name, Key=key, UploadId=upload_id, MultipartUpload={'Parts': parts})
+    # check extra client.complete_multipart_upload
+    client.complete_multipart_upload(Bucket=bucket_name, Key=key, UploadId=upload_id, MultipartUpload={'Parts': parts})
 
     response = client.head_bucket(Bucket=bucket_name)
     rgw_bytes_used = int(response['ResponseMetadata']['HTTPHeaders'].get('x-rgw-bytes-used', objlen))