diff --git a/nixos/lib/systemd-lib.nix b/nixos/lib/systemd-lib.nix
index c6c8753d5325..a21450708fe5 100644
--- a/nixos/lib/systemd-lib.nix
+++ b/nixos/lib/systemd-lib.nix
@@ -24,7 +24,7 @@ in rec {
         }
         ''
           name=${shellEscape name}
-          mkdir -p "$out/$(dirname "$name")"
+          mkdir -p "$out/$(dirname -- "$name")"
           echo -n "$text" > "$out/$name"
         ''
     else