diff --git a/nixos/tests/udisks2.nix b/nixos/tests/udisks2.nix
index 1f01cc6de4d6..6c4b71aaa2ed 100644
--- a/nixos/tests/udisks2.nix
+++ b/nixos/tests/udisks2.nix
@@ -34,7 +34,7 @@ in
 
       with lzma.open(
           "${stick}"
-      ) as data, open(machine.state_dir + "/usbstick.img", "wb") as stick:
+      ) as data, open(machine.state_dir / "usbstick.img", "wb") as stick:
           stick.write(data.read())
 
       machine.succeed("udisksctl info -b /dev/vda >&2")