diff --git a/pkgs/by-name/ca/casync/package.nix b/pkgs/by-name/ca/casync/package.nix
index 21c62cc44db6..9a1c009ab9b3 100644
--- a/pkgs/by-name/ca/casync/package.nix
+++ b/pkgs/by-name/ca/casync/package.nix
@@ -64,7 +64,8 @@ stdenv.mkDerivation {
     patchShebangs test/http-server.py
   '';
 
-  PKG_CONFIG_UDEV_UDEVDIR = "lib/udev";
+  env.PKG_CONFIG_UDEV_UDEVDIR = "lib/udev";
+
   mesonFlags =
     lib.optionals (!fuseSupport) [ "-Dfuse=false" ]
     ++ lib.optionals (!udevSupport) [ "-Dudev=false" ]