diff --git a/nixos/lib/systemd-lib.nix b/nixos/lib/systemd-lib.nix
index 61ac04eff288..585c4e514628 100644
--- a/nixos/lib/systemd-lib.nix
+++ b/nixos/lib/systemd-lib.nix
@@ -66,7 +66,7 @@ in rec {
       "Systemd ${group} field `${name}' must be a valid MAC address.";
 
   assertNetdevMacAddress = name: group: attr:
-    optional (attr ? ${name} && (! isMacAddress attr.${name} || attr.${name} != "none"))
+    optional (attr ? ${name} && (! isMacAddress attr.${name} && attr.${name} != "none"))
       "Systemd ${group} field `${name}` must be a valid MAC address or the special value `none`.";