diff --git a/nixos/modules/tasks/swraid.nix b/nixos/modules/tasks/swraid.nix
index 8985660d80a7..1174187062d7 100644
--- a/nixos/modules/tasks/swraid.nix
+++ b/nixos/modules/tasks/swraid.nix
@@ -67,7 +67,7 @@ in {
         $out/bin/mdadm --version
       '';
 
-      extraFiles."/etc/mdadm.conf" = mdadm_conf;
+      extraFiles."/etc/mdadm.conf".source = pkgs.writeText "mdadm.conf" mdadm_conf.text;
 
       systemd = {
         contents."/etc/mdadm.conf".text = mdadm_conf.text;
diff --git a/nixos/tests/systemd-initrd-swraid.nix b/nixos/tests/systemd-initrd-swraid.nix
index cb5b1cb4f535..d00e67b5705a 100644
--- a/nixos/tests/systemd-initrd-swraid.nix
+++ b/nixos/tests/systemd-initrd-swraid.nix
@@ -32,6 +32,9 @@ import ./make-test-python.nix ({ lib, pkgs, ... }: {
     };
 
     specialisation.boot-swraid.configuration.virtualisation.rootDevice = "/dev/disk/by-label/testraid";
+    # This protects against a regression. We do not have to switch to it.
+    # It's sufficient to trigger its evaluation.
+    specialisation.build-old-initrd.configuration.boot.initrd.systemd.enable = lib.mkForce false;
   };
 
   testScript = ''