diff --git a/pkgs/vivado/vivado.nix b/pkgs/vivado/vivado.nix
index 73f95c0..30b0710 100644
--- a/pkgs/vivado/vivado.nix
+++ b/pkgs/vivado/vivado.nix
@@ -6,19 +6,7 @@
   lib,
   passt,
   runtimeShell,
-  enableMacSpoofing ? false,
-  macAddress ?
-    if enableMacSpoofing then
-      lib.warn ''
-        In order for licensing to work, you need to manually provide your licensed machine's MAC address.
-        This can be done in two ways:
-          a) Set an env var `XILINX_NIC_ID=xx:xx:xx:xx:xx:xx`
-          b) Override the package `(vivado.override { macAddress = "xx:xx:xx:xx:xx:xx"; })`
-        If both are configured, the environment variable takes precedence.
-        Run `vlm` to see the current licensing status of your installation.
-      '' "aa:aa:aa:aa:aa:aa"
-    else
-      null,
+  macAddress ? null, # also controlled by XILINX_NIC_ID env var
   extraProfile ? "",
   extraPkgs ? pkgs: [ ],
 
@@ -316,36 +304,35 @@ buildFHSEnv (finalAttrs: rec {
     "--cap-add CAP_NET_ADMIN"
     "--cap-add CAP_NET_BIND_SERVICE"
   ];
-  profile =
-    let
-      XILINX_NIC_ID = lib.optionalString enableMacSpoofing ''
-        : ''${XILINX_NIC_ID:=${macAddress}}
-        export XILINX_NIC_ID
-      '';
-    in
-    ''
-      ${XILINX_NIC_ID}
-      export LC_NUMERIC="en_US.UTF-8"
-      export GDK_BACKEND=x11
-      export DISPLAY="''${DISPLAY:-:0}"
-      export _JAVA_AWT_WM_NONREPARENTING=1
-      export ELECTRON_OZONE_PLATFORM_HINT=x11
-      source ${unwrapped}/opt/Xilinx/${version}/Vivado/settings64.sh
-    ''
-    + extraProfile;
-  runScript =
-    if enableMacSpoofing then
-      (lib.concatStringsSep " " [
-        "${passt}/bin/pasta"
-        "--ns-mac-addr $XILINX_NIC_ID"
-        "--hostname $(hostname)"
-        "--runas $(whoami)"
-        "--ns-ifname eth0"
-        "--config-net"
-        "--netns-only"
-      ])
-    else
-      "";
+  profile = ''
+    ${lib.optionalString (!(isNull macAddress)) ''
+      : ''${XILINX_NIC_ID:=${macAddress}}
+    ''}
+    export LC_NUMERIC="en_US.UTF-8"
+    export GDK_BACKEND=x11
+    export DISPLAY="''${DISPLAY:-:0}"
+    export _JAVA_AWT_WM_NONREPARENTING=1
+    export ELECTRON_OZONE_PLATFORM_HINT=x11
+    source ${unwrapped}/opt/Xilinx/${version}/Vivado/settings64.sh
+    init_cmd=()
+    if ! [ -z "''${XILINX_NIC_ID}" ]; then
+      init_cmd+=(
+        '${passt}/bin/pasta'
+        '--ns-mac-addr'
+        "$XILINX_NIC_ID"
+        '--hostname'
+        "$(hostname)"
+        '--runas'
+        "$(whoami)"
+        '--ns-ifname'
+        'eth0'
+        '--config-net'
+        '--netns-only'
+      )
+    fi
+  ''
+  + extraProfile;
+  runScript = ''''${init_cmd[@]}'';
 
   inherit (unwrapped) meta;
 })