diff --git a/flake.nix b/flake.nix
index e8a84b0..6620438 100644
--- a/flake.nix
+++ b/flake.nix
@@ -104,7 +104,8 @@
         deploy-rs-pkg = null;
       })
       (_: super: {
-        inherit (super.callPackage ./pkgs/compress-drv.nix {}) compressDrvWeb;
+        compressDrv = super.callPackage ./pkgs/compress-drv {};
+        compressDrvWeb = super.callPackage ./pkgs/compress-drv/web.nix {};
 
         tmuxbash = super.callPackage ./pkgs/tmuxbash.nix {};
         btrfs-auto-snapshot = super.callPackage ./pkgs/btrfs-auto-snapshot.nix {};
@@ -357,10 +358,10 @@
                 };
               };
 
-              #compress-drv-tests = let
-              #  pkgs = import nixpkgs {inherit system;};
-              #in
-              #  pkgs.callPackage ./pkgs/compress-drv-tests.nix {};
+              compress-drv-test = let
+                pkgs = import nixpkgs {inherit system overlays;};
+              in
+                pkgs.callPackage ./pkgs/compress-drv/test.nix {};
             }
         )
         deploy-rs.lib;
diff --git a/pkgs/compress-drv.nix b/pkgs/compress-drv.nix
deleted file mode 100644
index ce5248f..0000000
--- a/pkgs/compress-drv.nix
+++ /dev/null
@@ -1,184 +0,0 @@
-{
-  lib,
-  runCommand,
-  xorg,
-  zopfli,
-  brotli,
-}: let
-  compressDrv = drv: {
-    formats,
-    compressors,
-    ...
-  } @ args: let
-    compressorMap = lib.filterAttrs (k: _: (lib.hasPrefix "compressor-" k)) args;
-    compressCommands =
-      map
-      (ext: let
-        prog = builtins.getAttr "compressor-${ext}" compressorMap;
-      in "tee >(xargs -I{} -n1 -P$NIX_BUILD_CORES ${prog})")
-      compressors;
-    formatsbar = builtins.concatStringsSep "|" formats;
-  in
-    runCommand "${drv.name}-compressed" {} ''
-      mkdir $out
-      ${xorg.lndir}/bin/lndir ${drv}/ $out/
-
-      find -L $out -type f -regextype posix-extended \
-        -iregex '.*\.(${formatsbar})' | \
-          ${builtins.concatStringsSep " | \\\n    " compressCommands}
-      find $out/
-    '';
-in {
-  /*
-  compressDrv compresses files in a given derivation.
-
-  Inputs:
-
-  - formats :: [String]
-
-      List of file extensions to compress.
-
-      Example: ["txt" "svg" "xml"]
-
-  - compressors :: [String]
-
-      A list of compressor names to use. Each element will need to have
-      an associated compressor in the same arguments (see below).
-
-      Example: ["gz" "zstd"]
-
-  - compressor-<EXTENSION> :: String
-
-      Map a desired extension (e.g. `gz`) to a compress program.
-
-      The compressor program that will be executed to get the `COMPRESSOR`
-      extension. The program is passed to xargs like this:
-
-        xargs -I{} -n1 ${prog}
-
-      Compressor must:
-      - read symlinks (thus --force is needed to gzip, zstd, xz).
-      - keep the original file in place (--keep).
-
-      Example compressor:
-
-        compressor-xz = "${xz}/bin/xz --force --keep {}";
-
-   See compressDrvWeb, which is a wrapper on top of compressDrv, for broader
-   use examples.
-  */
-
-  compressDrv = compressDrv;
-
-  /*
-  compressDrvWeb compresses a derivation for "web server" usage.
-
-  Useful when one wants to pre-compress certain static assets and pass them to
-  the web server. For example, `pkgs.gamja` creates this derivation:
-
-      /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/
-      ├── index.2fd01148.js
-      ├── index.2fd01148.js.map
-      ├── index.37aa9a8a.css
-      ├── index.37aa9a8a.css.map
-      ├── index.html
-      └── manifest.webmanifest
-
-  `pkgs.compressDrvWeb pkgs.gamja`:
-
-      /nix/store/f5ryid7zrw2hid7h9kil5g5j29q5r2f7-gamja-1.0.0-beta.9-compressed
-      ├── index.2fd01148.js -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.2fd01148.js
-      ├── index.2fd01148.js.br
-      ├── index.2fd01148.js.gz
-      ├── index.2fd01148.js.map -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.2fd01148.js.map
-      ├── index.2fd01148.js.map.br
-      ├── index.2fd01148.js.map.gz
-      ├── index.37aa9a8a.css -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.37aa9a8a.css
-      ├── index.37aa9a8a.css.br
-      ├── index.37aa9a8a.css.gz
-      ├── index.37aa9a8a.css.map -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.37aa9a8a.css.map
-      ├── index.37aa9a8a.css.map.br
-      ├── index.37aa9a8a.css.map.gz
-      ├── index.html -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.html
-      ├── index.html.br
-      ├── index.html.gz
-      ├── manifest.webmanifest -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/manifest.webmanifest
-      ├── manifest.webmanifest.br
-      └── manifest.webmanifest.gz
-
-
-  When this `-compressed` directory is passed to a properly configured web
-  server, it will serve those pre-compressed files:
-
-      $ curl -I -H 'Accept-Encoding: br' https://irc.example.org/
-      <...>
-      content-encoding: br
-      <...>
-
-  For example, a caddy configuration snippet for gamja to serve
-  the static assets (JS, CSS files) pre-compressed:
-
-      virtualHosts."irc.example.org".extraConfig = ''
-        root * ${pkgs.compressDrvWeb pkgs.gamja {}}
-        file_server browse {
-            precompressed br gzip
-        }
-      '';
-
-  This feature is also available in nginx via `ngx_brotli` and
-  `ngx_http_gzip_static_module`.
-
-  Inputs:
-  - formats :: [String]
-
-      List of file extensions to compress.
-
-      Default: common formats that compress well. The list may be appended
-      expanded.
-
-  - extraFormats :: [String]
-
-      Extra extensions to compress in addition to `formats`.
-
-  - compressors :: [String]
-
-      A list of compressor names to use. Each element will need to have
-      an associated compressor in the same arguments (see below).
-
-      Default: ["gz" "br"]
-
-    - extraCompressors :: [String]
-
-      Extra compressors in addition to `compressors`.
-
-  - compressor-<COMPRESSOR> :: String
-
-      Map a desired extension (e.g. `gz`) to a compress program.
-
-      The compressor program that will be executed to get the `COMPRESSOR`
-      extension. The program is passed to xargs like this:
-
-        xargs -I{} -n1 ${prog}
-
-      Default:
-
-        compressor-gz = "${zopfli}/bin/zopfli --keep {}";
-        compressor-br = "${brotli}/bin/brotli --keep --no-copy-stat {}";
-
-  */
-
-  compressDrvWeb = drv: {
-    formats ? ["css" "js" "svg" "ttf" "eot" "txt" "xml" "map" "html" "json" "webmanifest"],
-    extraFormats ? [],
-    compressors ? ["gz" "br"],
-    extraCompressors ? [],
-    ...
-  } @ args:
-    compressDrv drv ({
-        formats = formats ++ extraFormats;
-        compressors = compressors ++ extraCompressors;
-        compressor-gz = "${zopfli}/bin/zopfli --keep {}";
-        compressor-br = "${brotli}/bin/brotli --keep --no-copy-stat {}";
-      }
-      // lib.filterAttrs (k: _: (lib.hasPrefix "compressor-" k)) args);
-}
diff --git a/pkgs/compress-drv/default.nix b/pkgs/compress-drv/default.nix
new file mode 100644
index 0000000..254a0ef
--- /dev/null
+++ b/pkgs/compress-drv/default.nix
@@ -0,0 +1,76 @@
+/*
+compressDrv compresses files in a given derivation.
+
+Inputs:
+
+- formats :: [String]
+
+    List of file extensions to compress.
+
+    Example: ["txt" "svg" "xml"]
+
+- compressors :: [String]
+
+    A list of compressor names to use. Each element will need to have
+    an associated compressor in the same arguments (see below).
+
+    Example: ["gz" "zstd"]
+
+- compressor-<EXTENSION> :: String
+
+    Map a desired extension (e.g. `gz`) to a compress program.
+
+    The compressor program that will be executed to get the `COMPRESSOR`
+    extension. The program should have a single " {}", which will be the
+    replaced with the target filename.
+
+    Compressor must:
+    - read symlinks (thus --force is needed to gzip, zstd, xz).
+    - keep the original file in place (--keep).
+
+    Example compressor:
+
+      compressor-xz = "${xz}/bin/xz --force --keep {}";
+
+ See compressDrvWeb, which is a wrapper on top of compressDrv, for broader
+ use examples.
+*/
+{
+  lib,
+  runCommand,
+  parallel,
+  xorg,
+}: drv: {
+  formats,
+  compressors,
+  ...
+} @ args: let
+  validProg = ext: prog: let
+    matches = (builtins.length (builtins.split "\\{}" prog) - 1) / 2;
+  in
+    lib.assertMsg
+    (matches == 1)
+    "compressor-${ext} needs to have exactly one '{}', found ${builtins.toString matches}";
+  compressorMap = lib.filterAttrs (k: _: (lib.hasPrefix "compressor-" k)) args;
+  mkCmd = ext: prog: let
+    fname = builtins.replaceStrings ["{}"] ["\"$fname\""] prog;
+  in
+    assert validProg ext prog; "${parallel}/bin/sem --id $$ -P$NIX_BUILD_CORES ${fname}";
+  formatsPipe = builtins.concatStringsSep "|" formats;
+in
+  runCommand "${drv.name}-compressed" {} ''
+    mkdir $out
+    export PARALLEL_HOME=$(mktemp -d)
+    ${xorg.lndir}/bin/lndir ${drv}/ $out/
+
+    while IFS= read -d "" -r fname; do
+      ${
+      lib.concatMapStringsSep
+      "\n"
+      (ext: mkCmd ext (builtins.getAttr "compressor-${ext}" compressorMap))
+      compressors
+    }
+    done < <(find -L $out -print0 -type f -regextype posix-extended -iregex '.*\.(${formatsPipe})')
+
+    ${parallel}/bin/sem --id ''$$ --wait
+  ''
diff --git a/pkgs/compress-drv-tests.nix b/pkgs/compress-drv/test.nix
similarity index 66%
rename from pkgs/compress-drv-tests.nix
rename to pkgs/compress-drv/test.nix
index 5620126..b30e1b0 100644
--- a/pkgs/compress-drv-tests.nix
+++ b/pkgs/compress-drv/test.nix
@@ -1,13 +1,11 @@
 {
   gzip,
-  callPackage,
-  runCommandNoCC,
+  runCommand,
+  compressDrv,
 }: let
-  compressDrv = (callPackage ./compress-drv.nix {}).compressDrv;
-
-  example = runCommandNoCC "sample-drv" {} ''
+  example = runCommand "sample-drv" {} ''
     mkdir $out
-    echo 1 > $out/1.txt
+    echo 42 > $out/1.txt
     touch $out/2.png
   '';
   drv = compressDrv example {
@@ -16,7 +14,7 @@
     compressor-gz = "${gzip}/bin/gzip --force --keep --fast {}";
   };
 in
-  runCommandNoCC "test-compressDrv" {} ''
+  runCommand "test-compressDrv" {} ''
     set -ex
     find ${drv}
     test -h ${drv}/1.txt
diff --git a/pkgs/compress-drv/web.nix b/pkgs/compress-drv/web.nix
new file mode 100644
index 0000000..e6aa26f
--- /dev/null
+++ b/pkgs/compress-drv/web.nix
@@ -0,0 +1,113 @@
+/*
+compressDrvWeb compresses a derivation for common web server use.
+
+Useful when one wants to pre-compress certain static assets and pass them to
+the web server. For example, `pkgs.gamja` creates this derivation:
+
+    /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/
+    ├── index.2fd01148.js
+    ├── index.2fd01148.js.map
+    ├── index.37aa9a8a.css
+    ├── index.37aa9a8a.css.map
+    ├── index.html
+    └── manifest.webmanifest
+
+`pkgs.compressDrvWeb pkgs.gamja`:
+
+    /nix/store/f5ryid7zrw2hid7h9kil5g5j29q5r2f7-gamja-1.0.0-beta.9-compressed
+    ├── index.2fd01148.js -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.2fd01148.js
+    ├── index.2fd01148.js.br
+    ├── index.2fd01148.js.gz
+    ├── index.2fd01148.js.map -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.2fd01148.js.map
+    ├── index.2fd01148.js.map.br
+    ├── index.2fd01148.js.map.gz
+    ├── index.37aa9a8a.css -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.37aa9a8a.css
+    ├── index.37aa9a8a.css.br
+    ├── index.37aa9a8a.css.gz
+    ├── index.37aa9a8a.css.map -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.37aa9a8a.css.map
+    ├── index.37aa9a8a.css.map.br
+    ├── index.37aa9a8a.css.map.gz
+    ├── index.html -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/index.html
+    ├── index.html.br
+    ├── index.html.gz
+    ├── manifest.webmanifest -> /nix/store/2wn1qbk8gp4y2m8xvafxv1b2dcdqj8fz-gamja-1.0.0-beta.9/manifest.webmanifest
+    ├── manifest.webmanifest.br
+    └── manifest.webmanifest.gz
+
+
+When this `-compressed` directory is passed to a properly configured web
+server, it will serve those pre-compressed files:
+
+    $ curl -I -H 'Accept-Encoding: br' https://irc.example.org/
+    <...>
+    content-encoding: br
+    <...>
+
+For example, a caddy configuration snippet for gamja to serve
+the static assets (JS, CSS files) pre-compressed:
+
+    virtualHosts."irc.example.org".extraConfig = ''
+      root * ${pkgs.compressDrvWeb pkgs.gamja {}}
+      file_server browse {
+          precompressed br gzip
+      }
+    '';
+
+This feature is also available in nginx via `ngx_brotli` and
+`ngx_http_gzip_static_module`.
+
+Inputs:
+- formats :: [String]
+
+    List of file extensions to compress.
+
+    Default: common formats that compress well. The list may be expanded.
+
+- extraFormats :: [String]
+
+    Extra extensions to compress in addition to `formats`.
+
+- compressors :: [String]
+
+    A list of compressor names to use. Each element will need to have
+    an associated compressor in the same arguments (see below).
+
+    Default: ["gz" "br"]
+
+  - extraCompressors :: [String]
+
+    Extra compressors in addition to `compressors`.
+
+- compressor-<COMPRESSOR> :: String
+
+    Map a desired extension (e.g. `gz`) to a compress program.
+
+    The compressor program that will be executed to get the `COMPRESSOR`
+    extension. The program is passed to xargs like this:
+
+      xargs -I{} -n1 ${prog}
+
+    Default:
+
+      compressor-gz = "${zopfli}/bin/zopfli --keep {}";
+      compressor-br = "${brotli}/bin/brotli --keep --no-copy-stat {}";
+*/
+{
+  lib,
+  zopfli,
+  brotli,
+  compressDrv,
+}: drv: {
+  formats ? ["css" "js" "svg" "ttf" "eot" "txt" "xml" "map" "html" "json" "webmanifest"],
+  extraFormats ? [],
+  compressors ? ["gz" "br"],
+  extraCompressors ? [],
+  ...
+} @ args:
+compressDrv drv ({
+    formats = formats ++ extraFormats;
+    compressors = compressors ++ extraCompressors;
+    compressor-gz = "${zopfli}/bin/zopfli --keep {}";
+    compressor-br = "${brotli}/bin/brotli --keep --no-copy-stat {}";
+  }
+  // lib.filterAttrs (k: _: (lib.hasPrefix "compressor-" k)) args)