diff --git a/modules/services/hardware/udev.nix b/modules/services/hardware/udev.nix
index d558d2983cf9..e1a338d6ad8b 100644
--- a/modules/services/hardware/udev.nix
+++ b/modules/services/hardware/udev.nix
@@ -6,7 +6,7 @@ let
 
   inherit (pkgs) stdenv writeText procps;
 
-  udev = config.system.build.systemd;
+  udev = config.systemd.package;
 
   cfg = config.services.udev;
 
diff --git a/modules/services/hardware/upower.nix b/modules/services/hardware/upower.nix
index 54f5d03de391..5d1658adb75f 100644
--- a/modules/services/hardware/upower.nix
+++ b/modules/services/hardware/upower.nix
@@ -56,7 +56,7 @@ with pkgs.lib;
     # the daemon.
     powerManagement.resumeCommands =
       ''
-        ${config.system.build.systemd}/bin/systemctl try-restart upower
+        ${config.systemd.package}/bin/systemctl try-restart upower
       '';
 
   };
diff --git a/modules/services/misc/nix-gc.nix b/modules/services/misc/nix-gc.nix
index dc9fa85cf667..280450446016 100644
--- a/modules/services/misc/nix-gc.nix
+++ b/modules/services/misc/nix-gc.nix
@@ -49,7 +49,7 @@ in
   config = {
 
     services.cron.systemCronJobs = mkIf cfg.automatic (singleton
-      "${cfg.dates} root ${config.system.build.systemd}/bin/systemctl start nix-gc.service");
+      "${cfg.dates} root ${config.systemd.package}/bin/systemctl start nix-gc.service");
 
     systemd.services."nix-gc" =
       { description = "Nix Garbage Collector";
diff --git a/modules/services/networking/dhcpcd.nix b/modules/services/networking/dhcpcd.nix
index 533b719a6675..342253bac296 100644
--- a/modules/services/networking/dhcpcd.nix
+++ b/modules/services/networking/dhcpcd.nix
@@ -57,13 +57,13 @@ let
           # server hostnames in its config file, then it will never do
           # anything ever again ("couldn't resolve ..., giving up on
           # it"), so we silently lose time synchronisation.
-          ${config.system.build.systemd}/bin/systemctl try-restart ntpd.service
+          ${config.systemd.package}/bin/systemctl try-restart ntpd.service
 
-          ${config.system.build.systemd}/bin/systemctl start ip-up.target
+          ${config.systemd.package}/bin/systemctl start ip-up.target
       fi
 
       #if [ "$reason" = EXPIRE -o "$reason" = RELEASE -o "$reason" = NOCARRIER ] ; then
-      #    ${config.system.build.systemd}/bin/systemctl start ip-down.target
+      #    ${config.systemd.package}/bin/systemctl start ip-down.target
       #fi
     '';
 
@@ -126,7 +126,7 @@ in
     powerManagement.resumeCommands =
       ''
         # Tell dhcpcd to rebind its interfaces if it's running.
-        ${config.system.build.systemd}/bin/systemctl reload dhcpcd.service
+        ${config.systemd.package}/bin/systemctl reload dhcpcd.service
       '';
 
   };
diff --git a/modules/services/networking/networkmanager.nix b/modules/services/networking/networkmanager.nix
index d8198dd03298..0daa945c14ac 100644
--- a/modules/services/networking/networkmanager.nix
+++ b/modules/services/networking/networkmanager.nix
@@ -39,7 +39,7 @@ let
   ipUpScript = pkgs.writeScript "01nixos-ip-up" ''
     #!/bin/sh
     if test "$2" = "up"; then
-      ${config.system.build.systemd}/bin/systemctl start ip-up.target
+      ${config.systemd.package}/bin/systemctl start ip-up.target
     fi
   '';
 
diff --git a/modules/services/networking/wpa_supplicant.nix b/modules/services/networking/wpa_supplicant.nix
index 4f8ae55d2090..20752cdee259 100644
--- a/modules/services/networking/wpa_supplicant.nix
+++ b/modules/services/networking/wpa_supplicant.nix
@@ -124,7 +124,7 @@ in
 
     powerManagement.resumeCommands =
       ''
-        ${config.system.build.systemd}/bin/systemctl try-restart wpa_supplicant
+        ${config.systemd.package}/bin/systemctl try-restart wpa_supplicant
       '';
 
     assertions = [{ assertion = !cfg.userControlled.enable || cfg.interfaces != [];
diff --git a/modules/services/x11/display-managers/default.nix b/modules/services/x11/display-managers/default.nix
index 396311be49e1..1f842c0c9534 100644
--- a/modules/services/x11/display-managers/default.nix
+++ b/modules/services/x11/display-managers/default.nix
@@ -36,7 +36,7 @@ let
       # since presumably the desktop environment will handle these.
       if [ -z "$_INHIBITION_LOCK_TAKEN" ]; then
         export _INHIBITION_LOCK_TAKEN=1
-        exec ${config.system.build.systemd}/bin/systemd-inhibit --what=handle-lid-switch:handle-power-key "$0" "$sessionType"
+        exec ${config.systemd.package}/bin/systemd-inhibit --what=handle-lid-switch:handle-power-key "$0" "$sessionType"
       fi
 
       ${optionalString cfg.startOpenSSHAgent ''
diff --git a/modules/services/x11/display-managers/kdm.nix b/modules/services/x11/display-managers/kdm.nix
index 08ae667211d4..6a628ec124f2 100644
--- a/modules/services/x11/display-managers/kdm.nix
+++ b/modules/services/x11/display-managers/kdm.nix
@@ -12,8 +12,8 @@ let
   defaultConfig =
     ''
       [Shutdown]
-      HaltCmd=${config.system.build.systemd}/sbin/shutdown -h now
-      RebootCmd=${config.system.build.systemd}/sbin/shutdown -r now
+      HaltCmd=${config.systemd.package}/sbin/shutdown -h now
+      RebootCmd=${config.systemd.package}/sbin/shutdown -r now
       ${optionalString (config.system.boot.loader.id == "grub") ''
         BootManager=${if config.boot.loader.grub.version == 2 then "Grub2" else "Grub"}
       ''}
diff --git a/modules/services/x11/display-managers/slim.nix b/modules/services/x11/display-managers/slim.nix
index bc9aef101c7d..9e8b9391f45f 100644
--- a/modules/services/x11/display-managers/slim.nix
+++ b/modules/services/x11/display-managers/slim.nix
@@ -14,8 +14,8 @@ let
       xserver_arguments ${dmcfg.xserverArgs}
       sessions ${pkgs.lib.concatStringsSep "," (dmcfg.session.names ++ ["custom"])}
       login_cmd exec ${pkgs.stdenv.shell} ${dmcfg.session.script} "%session"
-      halt_cmd ${config.system.build.systemd}/sbin/shutdown -h now
-      reboot_cmd ${config.system.build.systemd}/sbin/shutdown -r now
+      halt_cmd ${config.systemd.package}/sbin/shutdown -h now
+      reboot_cmd ${config.systemd.package}/sbin/shutdown -r now
       ${optionalString (cfg.defaultUser != "") ("default_user " + cfg.defaultUser)}
       ${optionalString cfg.autoLogin "auto_login yes"}
     '';
diff --git a/modules/system/activation/top-level.nix b/modules/system/activation/top-level.nix
index 48c1c0be1896..e99b50a0309d 100644
--- a/modules/system/activation/top-level.nix
+++ b/modules/system/activation/top-level.nix
@@ -120,7 +120,7 @@ let
 
       echo -n "$kernelParams" > $out/kernel-params
       echo -n "$configurationName" > $out/configuration-name
-      echo -n "systemd ${toString config.system.build.systemd.interfaceVersion}" > $out/init-interface-version
+      echo -n "systemd ${toString config.systemd.package.interfaceVersion}" > $out/init-interface-version
       echo -n "$nixosVersion" > $out/nixos-version
 
       mkdir $out/fine-tune
@@ -149,7 +149,7 @@ let
     buildCommand = systemBuilder;
 
     inherit (pkgs) utillinux;
-    inherit (config.system.build) systemd;
+    systemd = config.systemd.package;
 
     inherit children;
     kernelParams =
diff --git a/modules/system/boot/kernel.nix b/modules/system/boot/kernel.nix
index 4776f4451f05..7744fd94a2c8 100644
--- a/modules/system/boot/kernel.nix
+++ b/modules/system/boot/kernel.nix
@@ -224,7 +224,7 @@ in
         serviceConfig =
           { Type = "oneshot";
             RemainAfterExit = true;
-            ExecStart = "${config.system.build.systemd}/lib/systemd/systemd-modules-load";
+            ExecStart = "${config.systemd.package}/lib/systemd/systemd-modules-load";
             # Ignore failed module loads.  Typically some of the
             # modules in ‘boot.kernelModules’ are "nice to have but
             # not required" (e.g. acpi-cpufreq), so we don't want to
diff --git a/modules/system/boot/stage-1.nix b/modules/system/boot/stage-1.nix
index b131867966ab..9743703ffbe6 100644
--- a/modules/system/boot/stage-1.nix
+++ b/modules/system/boot/stage-1.nix
@@ -9,7 +9,7 @@ with pkgs.lib;
 
 let
 
-  udev = config.system.build.systemd;
+  udev = config.systemd.package;
 
   options = {
 
diff --git a/modules/system/boot/systemd.nix b/modules/system/boot/systemd.nix
index 80957cd11930..b76367021206 100644
--- a/modules/system/boot/systemd.nix
+++ b/modules/system/boot/systemd.nix
@@ -8,7 +8,7 @@ let
 
   cfg = config.systemd;
 
-  systemd = pkgs.systemd;
+  systemd = cfg.package;
 
   makeUnit = name: unit:
     pkgs.runCommand "unit" { inherit (unit) text; }
@@ -340,6 +340,12 @@ in
 
   options = {
 
+    systemd.package = mkOption {
+      default = pkgs.systemd;
+      type = types.package;
+      description = "The systemd package.";
+    };
+
     systemd.units = mkOption {
       description = "Definition of systemd units.";
       default = {};
@@ -457,8 +463,6 @@ in
 
   config = {
 
-    system.build.systemd = systemd;
-
     system.build.units = units;
 
     environment.systemPackages = [ systemd ];
diff --git a/modules/tasks/kbd.nix b/modules/tasks/kbd.nix
index b0e222cd05eb..e4d22e94c80c 100644
--- a/modules/tasks/kbd.nix
+++ b/modules/tasks/kbd.nix
@@ -85,7 +85,7 @@ in
         serviceConfig =
           { Type = "oneshot";
             RemainAfterExit = true;
-            ExecStart = "${config.system.build.systemd}/lib/systemd/systemd-vconsole-setup /dev/tty1";
+            ExecStart = "${config.systemd.package}/lib/systemd/systemd-vconsole-setup /dev/tty1";
           };
         restartTriggers = [ vconsoleConf ];
       };
diff --git a/modules/tasks/network-interfaces.nix b/modules/tasks/network-interfaces.nix
index e8097e418c8b..49dd47251e5d 100644
--- a/modules/tasks/network-interfaces.nix
+++ b/modules/tasks/network-interfaces.nix
@@ -350,11 +350,11 @@ in
                     ip -4 addr add "${i.ipAddress}/${mask}" dev "${i.name}"
                     # Ensure that the default gateway remains set.
                     # (Flushing this interface may have removed it.)
-                    ${config.system.build.systemd}/bin/systemctl try-restart --no-block network-setup.service
+                    ${config.systemd.package}/bin/systemctl try-restart --no-block network-setup.service
                   else
                     echo "skipping configuring interface"
                   fi
-                  ${config.system.build.systemd}/bin/systemctl start ip-up.target
+                  ${config.systemd.package}/bin/systemctl start ip-up.target
                 ''
               + optionalString i.proxyARP
                 ''