diff --git a/pkgs/development/python-modules/willow/default.nix b/pkgs/development/python-modules/willow/default.nix
index cc67f380517e..f2ab1675d043 100644
--- a/pkgs/development/python-modules/willow/default.nix
+++ b/pkgs/development/python-modules/willow/default.nix
@@ -35,6 +35,8 @@ buildPythonPackage rec {
 
   nativeBuildInputs = [ flit-core ];
 
+  pythonRelaxDeps = [ "defusedxml" ];
+
   propagatedBuildInputs = [
     filetype
     defusedxml