diff --git a/pkgs/development/python-modules/unrardll/default.nix b/pkgs/development/python-modules/unrardll/default.nix
index 2eea89693ca8..1bacabbd1628 100644
--- a/pkgs/development/python-modules/unrardll/default.nix
+++ b/pkgs/development/python-modules/unrardll/default.nix
@@ -18,7 +18,9 @@ buildPythonPackage rec {
 
   buildInputs = [ unrar ];
 
-  NIX_CFLAGS_LINK = lib.optionalString stdenv.hostPlatform.isDarwin "-headerpad_max_install_names";
+  env = lib.optionalAttrs stdenv.hostPlatform.isDarwin {
+    NIX_CFLAGS_LINK = "-headerpad_max_install_names";
+  };
 
   postInstall = lib.optionalString stdenv.hostPlatform.isDarwin ''
     install_name_tool -change libunrar.so ${unrar}/lib/libunrar.so $out/lib/python*/site-packages/unrardll/unrar.*-darwin.so