diff --git a/lib/private/Files/ObjectStore/S3.php b/lib/private/Files/ObjectStore/S3.php
index 2d9119b5fc692..b1cd89388aea6 100644
--- a/lib/private/Files/ObjectStore/S3.php
+++ b/lib/private/Files/ObjectStore/S3.php
@@ -99,7 +99,7 @@ public function completeMultipartUpload(string $urn, string $uploadId, array $re
 		$stat = $this->getConnection()->headObject([
 			'Bucket' => $this->bucket,
 			'Key' => $urn,
-		]);
+		] + $this->getSSECParameters());
 		return (int)$stat->get('ContentLength');
 	}