diff --git a/pkgs/development/python-modules/pynest2d/default.nix b/pkgs/development/python-modules/pynest2d/default.nix
index 4e499fd47080..632101695f72 100644
--- a/pkgs/development/python-modules/pynest2d/default.nix
+++ b/pkgs/development/python-modules/pynest2d/default.nix
@@ -35,7 +35,7 @@ buildPythonPackage rec {
 
   strictDeps = true;
 
-  CLIPPER_PATH = "${clipper.out}";
+  env.CLIPPER_PATH = clipper.out;
 
   postPatch = ''
     sed -i 's#''${Python3_SITEARCH}#${placeholder "out"}/${python.sitePackages}#' cmake/SIPMacros.cmake