diff --git a/src/note.sol b/src/note.sol
index 73ade6f..b429cd8 100644
--- a/src/note.sol
+++ b/src/note.sol
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GNU-3
 /// note.sol -- the `note' modifier, for logging calls as events
 
 // This program is free software: you can redistribute it and/or modify