diff --git a/nixos/lib/test-driver/test-driver.py b/nixos/lib/test-driver/test-driver.py
index 2b8dffec7d5..c27947bc610 100644
--- a/nixos/lib/test-driver/test-driver.py
+++ b/nixos/lib/test-driver/test-driver.py
@@ -911,7 +911,7 @@ def subtest(name: str) -> Iterator[None]:
 if __name__ == "__main__":
     log = Logger()
 
-    vlan_nrs = list(dict.fromkeys(os.environ["VLANS"].split()))
+    vlan_nrs = list(dict.fromkeys(os.environ.get("VLANS", "").split()))
     vde_sockets = [create_vlan(v) for v in vlan_nrs]
     for nr, vde_socket, _, _ in vde_sockets:
         os.environ["QEMU_VDE_SOCKET_{}".format(nr)] = vde_socket