diff --git a/nixos/modules/virtualisation/virtualbox-image.nix b/nixos/modules/virtualisation/virtualbox-image.nix
index 2e30f4c62f97..f7c350f92216 100644
--- a/nixos/modules/virtualisation/virtualbox-image.nix
+++ b/nixos/modules/virtualisation/virtualbox-image.nix
@@ -2,112 +2,132 @@
 
 with lib;
 
-{
-  system.build.virtualBoxImage =
-    pkgs.vmTools.runInLinuxVM (
-      pkgs.runCommand "virtualbox-image"
-        { memSize = 768;
-          preVM =
-            ''
-              mkdir $out
-              diskImage=$out/image
-              ${pkgs.vmTools.qemu}/bin/qemu-img create -f raw $diskImage "10G"
-              mv closure xchg/
-            '';
-          postVM =
-            ''
-              echo "creating VirtualBox disk image..."
-              ${pkgs.vmTools.qemu}/bin/qemu-img convert -f raw -O vdi $diskImage $out/disk.vdi
-              rm $diskImage
-            '';
-          buildInputs = [ pkgs.utillinux pkgs.perl ];
-          exportReferencesGraph =
-            [ "closure" config.system.build.toplevel ];
-        }
-        ''
-          # Create a single / partition.
-          ${pkgs.parted}/sbin/parted /dev/vda mklabel msdos
-          ${pkgs.parted}/sbin/parted /dev/vda -- mkpart primary ext2 1M -1s
-          . /sys/class/block/vda1/uevent
-          mknod /dev/vda1 b $MAJOR $MINOR
+let
 
-          # Create an empty filesystem and mount it.
-          ${pkgs.e2fsprogs}/sbin/mkfs.ext4 -L nixos /dev/vda1
-          ${pkgs.e2fsprogs}/sbin/tune2fs -c 0 -i 0 /dev/vda1
-          mkdir /mnt
-          mount /dev/vda1 /mnt
+  cfg = config.virtualbox;
 
-          # The initrd expects these directories to exist.
-          mkdir /mnt/dev /mnt/proc /mnt/sys
-          mount --bind /proc /mnt/proc
-          mount --bind /dev /mnt/dev
-          mount --bind /sys /mnt/sys
+in {
 
-          # Copy all paths in the closure to the filesystem.
-          storePaths=$(perl ${pkgs.pathsFromGraph} /tmp/xchg/closure)
+  options = {
+    virtualbox = {
+      baseImageSize = mkOption {
+        type = types.str;
+        default = 10G;
+        description = ''
+          The size of the VirtualBox base image. The size string should be on
+          a format the qemu-img command accepts.
+        '';
+      };
+    };
+  };
 
-          echo "filling Nix store..."
-          mkdir -p /mnt/nix/store
-          set -f
-          cp -prd $storePaths /mnt/nix/store/
-
-          mkdir -p /mnt/etc/nix
-          echo 'build-users-group = ' > /mnt/etc/nix/nix.conf
-
-          # Register the paths in the Nix database.
-          printRegistration=1 perl ${pkgs.pathsFromGraph} /tmp/xchg/closure | \
-              chroot /mnt ${config.nix.package}/bin/nix-store --load-db
-
-          # Create the system profile to allow nixos-rebuild to work.
-          chroot /mnt ${config.nix.package}/bin/nix-env \
-              -p /nix/var/nix/profiles/system --set ${config.system.build.toplevel}
-
-          # `nixos-rebuild' requires an /etc/NIXOS.
-          mkdir -p /mnt/etc/nixos
-          touch /mnt/etc/NIXOS
-
-          # `switch-to-configuration' requires a /bin/sh
-          mkdir -p /mnt/bin
-          ln -s ${config.system.build.binsh}/bin/sh /mnt/bin/sh
-
-          # Generate the GRUB menu.
-          ln -s vda /dev/sda
-          chroot /mnt ${config.system.build.toplevel}/bin/switch-to-configuration boot
-
-          umount /mnt/proc /mnt/dev /mnt/sys
-          umount /mnt
-        ''
-    );
-
-  system.build.virtualBoxOVA = pkgs.runCommand "virtualbox-ova"
-    { buildInputs = [ pkgs.linuxPackages.virtualbox ];
-      vmName = "NixOS ${config.system.nixosVersion} (${pkgs.stdenv.system})";
-      fileName = "nixos-${config.system.nixosVersion}-${pkgs.stdenv.system}.ova";
-    }
-    ''
-      echo "creating VirtualBox VM..."
-      export HOME=$PWD
-      VBoxManage createvm --name "$vmName" --register \
-        --ostype ${if pkgs.stdenv.system == "x86_64-linux" then "Linux26_64" else "Linux26"}
-      VBoxManage modifyvm "$vmName" \
-        --memory 1536 --acpi on --vram 10 \
-        --nictype1 virtio --nic1 nat \
-        --audiocontroller ac97 --audio alsa \
-        --rtcuseutc on \
-        --usb on --mouse usbtablet
-      VBoxManage storagectl "$vmName" --name SATA --add sata --portcount 4 --bootable on --hostiocache on
-      VBoxManage storageattach "$vmName" --storagectl SATA --port 0 --device 0 --type hdd \
-        --medium ${config.system.build.virtualBoxImage}/disk.vdi
-
-      echo "exporting VirtualBox VM..."
-      mkdir -p $out
-      VBoxManage export "$vmName" --output "$out/$fileName"
-    '';
-
-  fileSystems."/".device = "/dev/disk/by-label/nixos";
-
-  boot.loader.grub.version = 2;
-  boot.loader.grub.device = "/dev/sda";
-
-  services.virtualbox.enable = true;
+  config = {
+    system.build.virtualBoxImage =
+      pkgs.vmTools.runInLinuxVM (
+        pkgs.runCommand "virtualbox-image"
+          { memSize = 768;
+            preVM =
+              ''
+                mkdir $out
+                diskImage=$out/image
+                ${pkgs.vmTools.qemu}/bin/qemu-img create -f raw $diskImage "${cfg.baseImageSize}"
+                mv closure xchg/
+              '';
+            postVM =
+              ''
+                echo "creating VirtualBox disk image..."
+                ${pkgs.vmTools.qemu}/bin/qemu-img convert -f raw -O vdi $diskImage $out/disk.vdi
+                rm $diskImage
+              '';
+            buildInputs = [ pkgs.utillinux pkgs.perl ];
+            exportReferencesGraph =
+              [ "closure" config.system.build.toplevel ];
+          }
+          ''
+            # Create a single / partition.
+            ${pkgs.parted}/sbin/parted /dev/vda mklabel msdos
+            ${pkgs.parted}/sbin/parted /dev/vda -- mkpart primary ext2 1M -1s
+            . /sys/class/block/vda1/uevent
+            mknod /dev/vda1 b $MAJOR $MINOR
+  
+            # Create an empty filesystem and mount it.
+            ${pkgs.e2fsprogs}/sbin/mkfs.ext4 -L nixos /dev/vda1
+            ${pkgs.e2fsprogs}/sbin/tune2fs -c 0 -i 0 /dev/vda1
+            mkdir /mnt
+            mount /dev/vda1 /mnt
+  
+            # The initrd expects these directories to exist.
+            mkdir /mnt/dev /mnt/proc /mnt/sys
+            mount --bind /proc /mnt/proc
+            mount --bind /dev /mnt/dev
+            mount --bind /sys /mnt/sys
+  
+            # Copy all paths in the closure to the filesystem.
+            storePaths=$(perl ${pkgs.pathsFromGraph} /tmp/xchg/closure)
+  
+            echo "filling Nix store..."
+            mkdir -p /mnt/nix/store
+            set -f
+            cp -prd $storePaths /mnt/nix/store/
+  
+            mkdir -p /mnt/etc/nix
+            echo 'build-users-group = ' > /mnt/etc/nix/nix.conf
+  
+            # Register the paths in the Nix database.
+            printRegistration=1 perl ${pkgs.pathsFromGraph} /tmp/xchg/closure | \
+                chroot /mnt ${config.nix.package}/bin/nix-store --load-db
+  
+            # Create the system profile to allow nixos-rebuild to work.
+            chroot /mnt ${config.nix.package}/bin/nix-env \
+                -p /nix/var/nix/profiles/system --set ${config.system.build.toplevel}
+  
+            # `nixos-rebuild' requires an /etc/NIXOS.
+            mkdir -p /mnt/etc/nixos
+            touch /mnt/etc/NIXOS
+  
+            # `switch-to-configuration' requires a /bin/sh
+            mkdir -p /mnt/bin
+            ln -s ${config.system.build.binsh}/bin/sh /mnt/bin/sh
+  
+            # Generate the GRUB menu.
+            ln -s vda /dev/sda
+            chroot /mnt ${config.system.build.toplevel}/bin/switch-to-configuration boot
+  
+            umount /mnt/proc /mnt/dev /mnt/sys
+            umount /mnt
+          ''
+      );
+  
+    system.build.virtualBoxOVA = pkgs.runCommand "virtualbox-ova"
+      { buildInputs = [ pkgs.linuxPackages.virtualbox ];
+        vmName = "NixOS ${config.system.nixosVersion} (${pkgs.stdenv.system})";
+        fileName = "nixos-${config.system.nixosVersion}-${pkgs.stdenv.system}.ova";
+      }
+      ''
+        echo "creating VirtualBox VM..."
+        export HOME=$PWD
+        VBoxManage createvm --name "$vmName" --register \
+          --ostype ${if pkgs.stdenv.system == "x86_64-linux" then "Linux26_64" else "Linux26"}
+        VBoxManage modifyvm "$vmName" \
+          --memory 1536 --acpi on --vram 10 \
+          --nictype1 virtio --nic1 nat \
+          --audiocontroller ac97 --audio alsa \
+          --rtcuseutc on \
+          --usb on --mouse usbtablet
+        VBoxManage storagectl "$vmName" --name SATA --add sata --portcount 4 --bootable on --hostiocache on
+        VBoxManage storageattach "$vmName" --storagectl SATA --port 0 --device 0 --type hdd \
+          --medium ${config.system.build.virtualBoxImage}/disk.vdi
+  
+        echo "exporting VirtualBox VM..."
+        mkdir -p $out
+        VBoxManage export "$vmName" --output "$out/$fileName"
+      '';
+  
+    fileSystems."/".device = "/dev/disk/by-label/nixos";
+  
+    boot.loader.grub.version = 2;
+    boot.loader.grub.device = "/dev/sda";
+  
+    services.virtualbox.enable = true;
+  };
 }