diff --git a/flake.nix b/flake.nix
index ea10b1c..71726a5 100644
--- a/flake.nix
+++ b/flake.nix
@@ -15,8 +15,11 @@
     };
   in
   {
-    packages = {
-      default = import ./orange.nix { inherit pkgs; };
+    packages = let 
+      orange = import ./sd-card.nix { inherit pkgs; };
+    in
+    {
+      default = orange;
     };
   }
   );
diff --git a/orange.nix b/orange.nix
deleted file mode 100644
index 7a904b1..0000000
--- a/orange.nix
+++ /dev/null
@@ -1,90 +0,0 @@
-{ pkgs }:
-
-let
-  imageName = "orange";
-  firmwarePartition = {
-    offset = 8;
-    id = "0xfeed3425";
-    name = "FIRMWARE";
-    size = 512;
-  };
-
-  rootfsImage = import ./rootfs.nix { inherit pkgs; };
-
-  configTxt = pkgs.writeText "config.txt" (builtins.readFile ./config.txt);
-  populateFirmwareCommands = ''
-    # Add config.txt
-    cp ${configTxt} firmware/config.txt
-
-    # Copy the firmware files
-    cp ${pkgs.raspberrypifw}/share/raspberrypi/boot/bootcode.bin firmware/
-    cp ${pkgs.raspberrypifw}/share/raspberrypi/boot/fixup*.dat firmware/
-    cp ${pkgs.raspberrypifw}/share/raspberrypi/boot/start*.elf firmware/
-
-    # Add pi3 specific files
-    cp ${pkgs.ubootRaspberryPi3_64bit}/u-boot.bin firmware/u-boot-rpi3.bin
-  '';
-in
-  pkgs.stdenv.mkDerivation {
-    name = imageName;
-
-    nativeBuildInputs = with pkgs; [ dosfstools e2fsprogs libfaketime mtools util-linux zstd ];
-
-    buildCommand = ''
-    mkdir -p $out/nix-support $out/sd-image
-    export img=$out/sd-image/${imageName}
-    echo "${pkgs.stdenv.buildPlatform.system}" > $out/nix-support/system
-    echo "file sd-image $img.zst" >> $out/nix-support/hydra-build-products
-    root_fs=${rootfsImage}
-
-    # Gap in front of the first partition, in MiB
-    gap=${toString firmwarePartition.offset}
-
-    # Create the image file sized to fit /boot/firmware and /, plus slack for the gap.
-    rootSizeBlocks=$(du -B 512 --apparent-size $root_fs | awk '{ print $1 }')
-    firmwareSizeBlocks=$((${toString firmwarePartition.size} * 1024 * 1024 / 512))
-    imageSize=$((rootSizeBlocks * 512 + firmwareSizeBlocks * 512 + gap * 1024 * 1024))
-    truncate -s $imageSize $img
-
-    # type=b is 'W95 FAT32', type=83 is 'Linux'.
-    # The "bootable" partition is where u-boot will look file for the bootloader
-    # information (dtbs, extlinux.conf file).
-    sfdisk $img <<EOF
-      label: dos
-      label-id: ${firmwarePartition.id}
-      start=''${gap}M, size=$firmwareSizeBlocks, type=b
-      start=$((gap + ${toString firmwarePartition.size}))M, type=83, bootable
-    EOF
-
-    # Copy the rootfs into the SD image
-    eval $(partx $img -o START,SECTORS --nr 2 --pairs)
-    dd conv=notrunc if=$root_fs of=$img seek=$START count=$SECTORS
-
-    # Create a FAT32 /boot/firmware partition of suitable size into firmware_part.img
-    eval $(partx $img -o START,SECTORS --nr 1 --pairs)
-    truncate -s $((SECTORS * 512)) firmware_part.img
-    mkfs.vfat --invariant -i ${toString firmwarePartition.size} -n ${firmwarePartition.name} firmware_part.img
-
-    # Populate the files intended for /boot/firmware
-    mkdir firmware
-    ${populateFirmwareCommands}
-    find firmware -exec touch --date=2000-01-01 {} +
-
-    # Copy the populated /boot/firmware into the SD image
-    cd firmware
-    # Force a fixed order in mcopy for better determinism, and avoid file globbing
-    for d in $(find . -type d -mindepth 1 | sort); do
-    faketime "2000-01-01 00:00:00" mmd -i ../firmware_part.img "::/$d"
-    done
-    for f in $(find . -type f | sort); do
-    mcopy -pvm -i ../firmware_part.img "$f" "::/$f"
-    done
-    cd ..
-
-    # Verify the FAT partition before copying it.
-    fsck.vfat -vn firmware_part.img
-
-    dd conv=notrunc if=firmware_part.img of=$img seek=$START count=$SECTORS
-    zstd -T$NIX_BUILD_CORES --rm $img
-    '';
-  }
diff --git a/rootfs.nix b/rootfs.nix
index fd315fb..9ee1adb 100644
--- a/rootfs.nix
+++ b/rootfs.nix
@@ -1,3 +1,12 @@
 { pkgs }:
 
-pkgs.runCommand "rootfs" {} "truncate -s 1M $out"
+pkgs.stdenv.mkDerivation {
+  name = "orange-rootfs.img.zstd";
+
+  nativeBuildInputs = with pkgs; [ zstd ];
+
+  buildCommand = ''
+    truncate -s 1M ./rootfs.img
+    zstd -T$NIX_BUILD_CORES ./rootfs.img -o $out
+  '';
+}
diff --git a/sd-card.nix b/sd-card.nix
new file mode 100644
index 0000000..0a57566
--- /dev/null
+++ b/sd-card.nix
@@ -0,0 +1,89 @@
+{ pkgs }:
+
+let
+  firmwarePartition = {
+    offset = 8;
+    id = "0xfeed3425";
+    name = "FIRMWARE";
+    size = 512;
+  };
+
+  rootfsImage = import ./rootfs.nix { inherit pkgs; };
+
+  configTxt = pkgs.writeText "config.txt" (builtins.readFile ./config.txt);
+  populateFirmwareCommands = ''
+    # Add config.txt
+    cp ${configTxt} firmware/config.txt
+
+    # Copy the firmware files
+    cp ${pkgs.raspberrypifw}/share/raspberrypi/boot/bootcode.bin firmware/
+    cp ${pkgs.raspberrypifw}/share/raspberrypi/boot/fixup*.dat firmware/
+    cp ${pkgs.raspberrypifw}/share/raspberrypi/boot/start*.elf firmware/
+
+    # Add pi3 specific files
+    cp ${pkgs.ubootRaspberryPi3_64bit}/u-boot.bin firmware/u-boot-rpi3.bin
+  '';
+in
+  pkgs.stdenv.mkDerivation {
+    name = "orange";
+
+    nativeBuildInputs = with pkgs; [ dosfstools e2fsprogs libfaketime mtools util-linux zstd ];
+
+    buildCommand = ''
+      img=./sd-card.img
+      root_fs=./rootfs.img
+      zstd -d --no-progress "${rootfsImage}" -o $root_fs
+
+      # Gap in front of the first partition, in MiB
+      gap=${toString firmwarePartition.offset}
+
+      # Create the image file sized to fit /boot/firmware and /, plus slack for the gap.
+      rootSizeBlocks=$(du -B 512 --apparent-size $root_fs | awk '{ print $1 }')
+      firmwareSizeBlocks=$((${toString firmwarePartition.size} * 1024 * 1024 / 512))
+      imageSize=$((rootSizeBlocks * 512 + firmwareSizeBlocks * 512 + gap * 1024 * 1024))
+      truncate -s $imageSize $img
+
+      # type=b is 'W95 FAT32', type=83 is 'Linux'.
+      # The "bootable" partition is where u-boot will look file for the bootloader
+      # information (dtbs, extlinux.conf file).
+      sfdisk $img <<EOF
+        label: dos
+        label-id: ${firmwarePartition.id}
+        start=''${gap}M, size=$firmwareSizeBlocks, type=b
+        start=$((gap + ${toString firmwarePartition.size}))M, type=83, bootable
+      EOF
+
+      # Copy the rootfs into the SD image
+      eval $(partx $img -o START,SECTORS --nr 2 --pairs)
+      dd conv=notrunc if=$root_fs of=$img seek=$START count=$SECTORS
+
+      # Create a FAT32 /boot/firmware partition of suitable size into firmware_part.img
+      eval $(partx $img -o START,SECTORS --nr 1 --pairs)
+      truncate -s $((SECTORS * 512)) firmware_part.img
+      mkfs.vfat --invariant -i ${toString firmwarePartition.size} -n ${firmwarePartition.name} firmware_part.img
+
+      # Populate the files intended for /boot/firmware
+      mkdir firmware
+      ${populateFirmwareCommands}
+      find firmware -exec touch --date=2000-01-01 {} +
+
+      # Copy the populated /boot/firmware into the SD image
+      cd firmware
+      # Force a fixed order in mcopy for better determinism, and avoid file globbing
+      for d in $(find . -type d -mindepth 1 | sort); do
+      faketime "2000-01-01 00:00:00" mmd -i ../firmware_part.img "::/$d"
+      done
+      for f in $(find . -type f | sort); do
+      mcopy -pvm -i ../firmware_part.img "$f" "::/$f"
+      done
+      cd ..
+
+      # Verify the FAT partition before copying it.
+      fsck.vfat -vn firmware_part.img
+
+      dd conv=notrunc if=firmware_part.img of=$img seek=$START count=$SECTORS
+
+      mkdir $out
+      zstd -T$NIX_BUILD_CORES $img -o $out/orange.img.zstd
+    '';
+  }