diff --git a/teuthida/__init__.py b/teuthida/__init__.py
index ac0200e..ac705ae 100644
--- a/teuthida/__init__.py
+++ b/teuthida/__init__.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: MIT
+
 from amaranth import *
 from enum import IntEnum
 
diff --git a/teuthida/gen.py b/teuthida/gen.py
index 57368e7..00728f6 100644
--- a/teuthida/gen.py
+++ b/teuthida/gen.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: MIT
+
 from amaranth.back import verilog
 from . import Cpu
 
diff --git a/teuthida/sim.py b/teuthida/sim.py
index fc635a1..9327f93 100644
--- a/teuthida/sim.py
+++ b/teuthida/sim.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: MIT
+
 from amaranth import *
 from amaranth.sim import *
 from . import Cpu, PipelineStage