diff --git a/rabbit.egg b/rabbit.egg
index 7da20a6..8e03baf 100644
--- a/rabbit.egg
+++ b/rabbit.egg
@@ -1,6 +1,6 @@
 ;; -*- lisp-data -*-
 ((synopsis "Rabbit stream cipher.")
- (license "Public Domain")
+ (license "Unlicense")
  (category crypt)
  (test-dependencies test)
  (maintainer "Lilianna Smólska")
diff --git a/rabbit.scm b/rabbit.scm
index 7fcfd67..30664af 100644
--- a/rabbit.scm
+++ b/rabbit.scm
@@ -4,6 +4,8 @@
 ;; key is 128 bit == 16 characters
 ;; iv is 64 bit = 8 characters
 
+;;; SPDX-License-Identifier: Unlicense
+
 ;; Based on lambdanative rabbit lib, ported to Chicken Scheme by Ivan Raikov
 
 (define debuglevel (make-parameter 0))
diff --git a/rabbit.sld b/rabbit.sld
index b68cafa..ad8a5f2 100644
--- a/rabbit.sld
+++ b/rabbit.sld
@@ -1,3 +1,4 @@
+;;; SPDX-License-Identifier: Unlicense
 (define-library rabbit
   (import
    (scheme base)
diff --git a/rabbitlib.c b/rabbitlib.c
index aaf1f47..b2506a0 100644
--- a/rabbitlib.c
+++ b/rabbitlib.c
@@ -1,6 +1,7 @@
 // Rabbit stream cipher 
 // written by Martin Boesgaard, Mette Vesterager, Thomas Christensen and Erik Zenner
 // public domain
+// SPDX-License-Identifier: Unlicense
 
 #include <stdio.h>
 #include <stdlib.h>