diff --git a/alioth/src/firmware/acpi/reg.rs b/alioth/src/firmware/acpi/reg.rs
index d8e9de49..1e4c8dd8 100644
--- a/alioth/src/firmware/acpi/reg.rs
+++ b/alioth/src/firmware/acpi/reg.rs
@@ -1,4 +1,5 @@
 // Copyright 2024 Google LLC
+// Copyright © 2019 Intel Corporation
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -63,6 +64,9 @@ impl Mmio for FadtSleepControl {
     }
 }
 
+// The following AcpiPmTimer implementation is derived from Cloud Hypervisor.
+// Copyright © 2019 Intel Corporation
+
 /// Power Management Timer
 ///
 /// ACPI v6.5, Sec. 4.8.2.1