diff --git a/README.md b/README.md
index a4592d70..35519891 100644
--- a/README.md
+++ b/README.md
@@ -180,6 +180,7 @@ To use an external S3 compatible object store as primary storage, set the follow
 - `OBJECTSTORE_S3_LEGACYAUTH` (default: `false`): Not required for AWS S3
 - `OBJECTSTORE_S3_OBJECT_PREFIX` (default: `urn:oid:`): Prefix to prepend to the fileid
 - `OBJECTSTORE_S3_AUTOCREATE` (default: `true`): Create the container if it does not exist
+- `OBJECTSTORE_S3_SSE_C_KEY`: Server side encryption key - must be a base64 encoded string with a maximum length of 32 bytes
 
 Check the [Nextcloud documentation](https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/primary_storage.html#simple-storage-service-s3) for more information.