diff --git a/nixos/modules/config/swap.nix b/nixos/modules/config/swap.nix
index 5c812a9226e8..0a7e45bffb26 100644
--- a/nixos/modules/config/swap.nix
+++ b/nixos/modules/config/swap.nix
@@ -275,12 +275,11 @@ in
                 ''}
                 ${optionalString sw.randomEncryption.enable ''
                   cryptsetup plainOpen -c ${sw.randomEncryption.cipher} -d ${sw.randomEncryption.source} \
-                '' + concatMapStrings (arg: arg + " \\\n") (flatten [
-                  (optional (sw.randomEncryption.sectorSize != null) "--sector-size=${toString sw.randomEncryption.sectorSize}")
-                  (optional (sw.randomEncryption.keySize != null) "--key-size=${toString sw.randomEncryption.keySize}")
-                  (optional sw.randomEncryption.allowDiscards "--allow-discards")
-                ]) + ''
-                  ${sw.device} ${sw.deviceName}
+                  ${concatStringsSep " \\\n" (flatten [
+                    (optional (sw.randomEncryption.sectorSize != null) "--sector-size=${toString sw.randomEncryption.sectorSize}")
+                    (optional (sw.randomEncryption.keySize != null) "--key-size=${toString sw.randomEncryption.keySize}")
+                    (optional sw.randomEncryption.allowDiscards "--allow-discards")
+                  ])} ${sw.device} ${sw.deviceName}
                   mkswap ${sw.realDevice}
                 ''}
               '';
diff --git a/nixos/tests/swap-file-btrfs.nix b/nixos/tests/swap-file-btrfs.nix
index d9fcd2be1160..35b9fb4fa50a 100644
--- a/nixos/tests/swap-file-btrfs.nix
+++ b/nixos/tests/swap-file-btrfs.nix
@@ -32,6 +32,8 @@ import ./make-test-python.nix ({ lib, ... }:
 
   testScript = ''
     machine.wait_for_unit('var-swapfile.swap')
+    # Ensure the swap file creation script ran to completion without failing when creating the swap file
+    machine.fail("systemctl is-failed --quiet mkswap-var-swapfile.service")
     machine.succeed("stat --file-system --format=%T /var/swapfile | grep btrfs")
     # First run. Auto creation.
     machine.succeed("swapon --show | grep /var/swapfile")
@@ -41,6 +43,8 @@ import ./make-test-python.nix ({ lib, ... }:
 
     # Second run. Use it as-is.
     machine.wait_for_unit('var-swapfile.swap')
+    # Ensure the swap file creation script ran to completion without failing when the swap file already exists
+    machine.fail("systemctl is-failed --quiet mkswap-var-swapfile.service")
     machine.succeed("swapon --show | grep /var/swapfile")
   '';
 })