diff --git a/scripts/imgtool/keys/x25519.py b/scripts/imgtool/keys/x25519.py
index adb68a1..a31cb3f 100644
--- a/scripts/imgtool/keys/x25519.py
+++ b/scripts/imgtool/keys/x25519.py
@@ -2,6 +2,8 @@
 X25519 key management
 """
 
+# SPDX-License-Identifier: Apache-2.0
+
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric import x25519