diff --git a/include/crypto/null.h b/include/crypto/null.h
index 3f0c59fb..5757c0a 100644
--- a/include/crypto/null.h
+++ b/include/crypto/null.h
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* Values for NULL algorithms */
 
 #ifndef _CRYPTO_NULL_H