diff --git a/pkgs/development/python-modules/duet/default.nix b/pkgs/development/python-modules/duet/default.nix
index c80bce22ef2c..d177bdbf7f54 100644
--- a/pkgs/development/python-modules/duet/default.nix
+++ b/pkgs/development/python-modules/duet/default.nix
@@ -36,5 +36,6 @@ buildPythonPackage rec {
     description = "Simple future-based async library for python";
     homepage = "https://github.com/google/duet";
     maintainers = [ ];
+    license = lib.licenses.asl20;
   };
 }