diff --git a/src/backend/kms/session_fd.rs b/src/backend/kms/session_fd.rs
index e41fd6e2..78576aec 100644
--- a/src/backend/kms/session_fd.rs
+++ b/src/backend/kms/session_fd.rs
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-3.0-only
+
 use smithay::reexports::nix::unistd::close;
 use std::{
     fmt,