diff --git a/codecs/oxipng/Cargo.toml b/codecs/oxipng/Cargo.toml
index a5c1273e..85e408aa 100644
--- a/codecs/oxipng/Cargo.toml
+++ b/codecs/oxipng/Cargo.toml
@@ -12,13 +12,16 @@ crate-type = ["cdylib"]
 oxipng = { version = "3.0.0", default-features = false, features = ["parallel"] }
 wasm-bindgen = "0.2.64"
 log = { version = "0.4", features = ["release_max_level_off"] }
-rayon = "1.3.0"
-crossbeam-deque = "0.7.3"
-once_cell = "1.3.1"
+rayon = { version = "1.3.0", optional = true }
+crossbeam-deque = { version = "0.7.3", optional = true }
+once_cell = { version = "1.3.1", optional = true }
 
 [profile.release]
 lto = true
 opt-level = "s"
 
+[features]
+parallel = ["oxipng/parallel", "rayon", "crossbeam-deque", "once_cell"]
+
 [package.metadata.wasm-pack.profile.release]
 wasm-opt = ["-O", "--no-validation"]
diff --git a/codecs/oxipng/Dockerfile b/codecs/oxipng/Dockerfile
index 5448d170..089be3c7 100644
--- a/codecs/oxipng/Dockerfile
+++ b/codecs/oxipng/Dockerfile
@@ -1,4 +1,4 @@
-FROM rust
+FROM rustlang/rust:nightly
 RUN rustup target add wasm32-unknown-unknown
 RUN curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
 
diff --git a/codecs/oxipng/build.sh b/codecs/oxipng/build.sh
index ebe32368..766fb4ba 100644
--- a/codecs/oxipng/build.sh
+++ b/codecs/oxipng/build.sh
@@ -6,9 +6,11 @@ echo "============================================="
 echo "Compiling wasm"
 echo "============================================="
 (
-  rm -rf pkg
-  CC=/opt/wasi-sdk/bin/clang RUSTFLAGS='-C target-feature=+atomics,+bulk-memory' rustup run nightly wasm-pack build -t web -- -Z build-std=panic_abort,std
-  rm pkg/.gitignore
+  export CC=/opt/wasi-sdk/bin/clang
+  rm -rf pkg,{-parallel}
+  wasm-pack build -t web
+  RUSTFLAGS='-C target-feature=+atomics,+bulk-memory' wasm-pack build -t web -d pkg-parallel -- -Z build-std=panic_abort,std --features=parallel
+  rm pkg{,-parallel}/.gitignore
 )
 echo "============================================="
 echo "Compiling wasm  done"
diff --git a/codecs/oxipng/pkg-parallel/oxipng.d.ts b/codecs/oxipng/pkg-parallel/oxipng.d.ts
new file mode 100644
index 00000000..4e9b03de
--- /dev/null
+++ b/codecs/oxipng/pkg-parallel/oxipng.d.ts
@@ -0,0 +1,46 @@
+/* tslint:disable */
+/* eslint-disable */
+/**
+* @returns {any} 
+*/
+export function worker_initializer(): any;
+/**
+* @param {number} num 
+*/
+export function start_main_thread(num: number): void;
+/**
+*/
+export function start_worker_thread(): void;
+/**
+* @param {Uint8Array} data 
+* @param {number} level 
+* @returns {Uint8Array} 
+*/
+export function optimise(data: Uint8Array, level: number): Uint8Array;
+
+export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;
+
+export interface InitOutput {
+  readonly worker_initializer: () => number;
+  readonly start_main_thread: (a: number) => void;
+  readonly start_worker_thread: () => void;
+  readonly optimise: (a: number, b: number, c: number, d: number) => void;
+  readonly malloc: (a: number) => number;
+  readonly free: (a: number) => void;
+  readonly __wbindgen_export_0: WebAssembly.Memory;
+  readonly __wbindgen_malloc: (a: number) => number;
+  readonly __wbindgen_free: (a: number, b: number) => void;
+  readonly __wbindgen_start: () => void;
+}
+
+/**
+* If `module_or_path` is {RequestInfo} or {URL}, makes a request and
+* for everything else, calls `WebAssembly.instantiate` directly.
+*
+* @param {InitInput | Promise<InitInput>} module_or_path
+* @param {WebAssembly.Memory} maybe_memory
+*
+* @returns {Promise<InitOutput>}
+*/
+export default function init (module_or_path?: InitInput | Promise<InitInput>, maybe_memory: WebAssembly.Memory): Promise<InitOutput>;
+        
\ No newline at end of file
diff --git a/codecs/oxipng/pkg-parallel/oxipng.js b/codecs/oxipng/pkg-parallel/oxipng.js
new file mode 100644
index 00000000..46033e33
--- /dev/null
+++ b/codecs/oxipng/pkg-parallel/oxipng.js
@@ -0,0 +1,174 @@
+
+let wasm;
+let memory;
+
+const heap = new Array(32).fill(undefined);
+
+heap.push(undefined, null, true, false);
+
+let heap_next = heap.length;
+
+function addHeapObject(obj) {
+    if (heap_next === heap.length) heap.push(heap.length + 1);
+    const idx = heap_next;
+    heap_next = heap[idx];
+
+    heap[idx] = obj;
+    return idx;
+}
+
+let cachedTextDecoder = new TextDecoder('utf-8', { ignoreBOM: true, fatal: true });
+
+cachedTextDecoder.decode();
+
+let cachegetUint8Memory0 = null;
+function getUint8Memory0() {
+    if (cachegetUint8Memory0 === null || cachegetUint8Memory0.buffer !== wasm.__wbindgen_export_0.buffer) {
+        cachegetUint8Memory0 = new Uint8Array(wasm.__wbindgen_export_0.buffer);
+    }
+    return cachegetUint8Memory0;
+}
+
+function getStringFromWasm0(ptr, len) {
+    return cachedTextDecoder.decode(getUint8Memory0().slice(ptr, ptr + len));
+}
+
+function getObject(idx) { return heap[idx]; }
+
+function dropObject(idx) {
+    if (idx < 36) return;
+    heap[idx] = heap_next;
+    heap_next = idx;
+}
+
+function takeObject(idx) {
+    const ret = getObject(idx);
+    dropObject(idx);
+    return ret;
+}
+/**
+* @returns {any}
+*/
+export function worker_initializer() {
+    var ret = wasm.worker_initializer();
+    return takeObject(ret);
+}
+
+/**
+* @param {number} num
+*/
+export function start_main_thread(num) {
+    wasm.start_main_thread(num);
+}
+
+/**
+*/
+export function start_worker_thread() {
+    wasm.start_worker_thread();
+}
+
+let WASM_VECTOR_LEN = 0;
+
+function passArray8ToWasm0(arg, malloc) {
+    const ptr = malloc(arg.length * 1);
+    getUint8Memory0().set(arg, ptr / 1);
+    WASM_VECTOR_LEN = arg.length;
+    return ptr;
+}
+
+let cachegetInt32Memory0 = null;
+function getInt32Memory0() {
+    if (cachegetInt32Memory0 === null || cachegetInt32Memory0.buffer !== wasm.__wbindgen_export_0.buffer) {
+        cachegetInt32Memory0 = new Int32Array(wasm.__wbindgen_export_0.buffer);
+    }
+    return cachegetInt32Memory0;
+}
+
+function getArrayU8FromWasm0(ptr, len) {
+    return getUint8Memory0().subarray(ptr / 1, ptr / 1 + len);
+}
+/**
+* @param {Uint8Array} data
+* @param {number} level
+* @returns {Uint8Array}
+*/
+export function optimise(data, level) {
+    var ptr0 = passArray8ToWasm0(data, wasm.__wbindgen_malloc);
+    var len0 = WASM_VECTOR_LEN;
+    wasm.optimise(8, ptr0, len0, level);
+    var r0 = getInt32Memory0()[8 / 4 + 0];
+    var r1 = getInt32Memory0()[8 / 4 + 1];
+    var v1 = getArrayU8FromWasm0(r0, r1).slice();
+    wasm.__wbindgen_free(r0, r1 * 1);
+    return v1;
+}
+
+async function load(module, imports, maybe_memory) {
+    if (typeof Response === 'function' && module instanceof Response) {
+        memory = imports.wbg.memory = new WebAssembly.Memory({initial:17,maximum:16384,shared:true});
+        if (typeof WebAssembly.instantiateStreaming === 'function') {
+            try {
+                return await WebAssembly.instantiateStreaming(module, imports);
+
+            } catch (e) {
+                if (module.headers.get('Content-Type') != 'application/wasm') {
+                    console.warn("`WebAssembly.instantiateStreaming` failed because your server does not serve wasm with `application/wasm` MIME type. Falling back to `WebAssembly.instantiate` which is slower. Original error:\n", e);
+
+                } else {
+                    throw e;
+                }
+            }
+        }
+
+        const bytes = await module.arrayBuffer();
+        return await WebAssembly.instantiate(bytes, imports);
+
+    } else {
+        memory = imports.wbg.memory = maybe_memory;
+        const instance = await WebAssembly.instantiate(module, imports);
+
+        if (instance instanceof WebAssembly.Instance) {
+            return { instance, module };
+
+        } else {
+            return instance;
+        }
+    }
+}
+
+async function init(input, maybe_memory) {
+    if (typeof input === 'undefined') {
+        input = import.meta.url.replace(/\.js$/, '_bg.wasm');
+    }
+    const imports = {};
+    imports.wbg = {};
+    imports.wbg.__wbindgen_module = function() {
+        var ret = init.__wbindgen_wasm_module;
+        return addHeapObject(ret);
+    };
+    imports.wbg.__wbindgen_memory = function() {
+        var ret = wasm.__wbindgen_export_0;
+        return addHeapObject(ret);
+    };
+    imports.wbg.__wbg_of_9335425aa94288f5 = function(arg0, arg1) {
+        var ret = Array.of(takeObject(arg0), takeObject(arg1));
+        return addHeapObject(ret);
+    };
+    imports.wbg.__wbindgen_throw = function(arg0, arg1) {
+        throw new Error(getStringFromWasm0(arg0, arg1));
+    };
+
+    if (typeof input === 'string' || (typeof Request === 'function' && input instanceof Request) || (typeof URL === 'function' && input instanceof URL)) {
+        input = fetch(input);
+    }
+
+    const { instance, module } = await load(await input, imports, maybe_memory);
+
+    wasm = instance.exports;
+    init.__wbindgen_wasm_module = module;
+    wasm.__wbindgen_start();
+    return wasm;
+}
+
+export default init;
+
diff --git a/codecs/oxipng/pkg-parallel/oxipng_bg.d.ts b/codecs/oxipng/pkg-parallel/oxipng_bg.d.ts
new file mode 100644
index 00000000..832b7200
--- /dev/null
+++ b/codecs/oxipng/pkg-parallel/oxipng_bg.d.ts
@@ -0,0 +1,12 @@
+/* tslint:disable */
+/* eslint-disable */
+export function worker_initializer(): number;
+export function start_main_thread(a: number): void;
+export function start_worker_thread(): void;
+export function optimise(a: number, b: number, c: number, d: number): void;
+export function malloc(a: number): number;
+export function free(a: number): void;
+export const __wbindgen_export_0: WebAssembly.Memory;
+export function __wbindgen_malloc(a: number): number;
+export function __wbindgen_free(a: number, b: number): void;
+export function __wbindgen_start(): void;
diff --git a/codecs/oxipng/pkg-parallel/oxipng_bg.wasm b/codecs/oxipng/pkg-parallel/oxipng_bg.wasm
new file mode 100644
index 00000000..2a02f110
Binary files /dev/null and b/codecs/oxipng/pkg-parallel/oxipng_bg.wasm differ
diff --git a/codecs/oxipng/pkg-parallel/package.json b/codecs/oxipng/pkg-parallel/package.json
new file mode 100644
index 00000000..5dd8df18
--- /dev/null
+++ b/codecs/oxipng/pkg-parallel/package.json
@@ -0,0 +1,15 @@
+{
+  "name": "oxipng",
+  "collaborators": [
+    "Ingvar Stepanyan <me@rreverser.com>"
+  ],
+  "version": "0.1.0",
+  "files": [
+    "oxipng_bg.wasm",
+    "oxipng.js",
+    "oxipng.d.ts"
+  ],
+  "module": "oxipng.js",
+  "types": "oxipng.d.ts",
+  "sideEffects": false
+}
\ No newline at end of file
diff --git a/codecs/oxipng/pkg/oxipng_bg.wasm b/codecs/oxipng/pkg/oxipng_bg.wasm
new file mode 100644
index 00000000..a6fef1ee
Binary files /dev/null and b/codecs/oxipng/pkg/oxipng_bg.wasm differ
diff --git a/codecs/oxipng/pkg/squoosh_oxipng.d.ts b/codecs/oxipng/pkg/squoosh_oxipng.d.ts
index 58683e41..ff57ceda 100644
--- a/codecs/oxipng/pkg/squoosh_oxipng.d.ts
+++ b/codecs/oxipng/pkg/squoosh_oxipng.d.ts
@@ -1,36 +1,21 @@
 /* tslint:disable */
 /* eslint-disable */
 /**
-* @returns {any}
-*/
-export function worker_initializer(): any;
-/**
-* @param {number} num
-*/
-export function start_main_thread(num: number): void;
-/**
-*/
-export function start_worker_thread(): void;
-/**
-* @param {Uint8Array} data
-* @param {number} level
-* @returns {Uint8Array}
+* @param {Uint8Array} data 
+* @param {number} level 
+* @returns {Uint8Array} 
 */
 export function optimise(data: Uint8Array, level: number): Uint8Array;
 
 export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;
 
 export interface InitOutput {
-  readonly worker_initializer: () => number;
-  readonly start_main_thread: (a: number) => void;
-  readonly start_worker_thread: () => void;
+  readonly memory: WebAssembly.Memory;
   readonly optimise: (a: number, b: number, c: number, d: number) => void;
   readonly malloc: (a: number) => number;
   readonly free: (a: number) => void;
-  readonly __wbindgen_export_0: WebAssembly.Memory;
   readonly __wbindgen_malloc: (a: number) => number;
   readonly __wbindgen_free: (a: number, b: number) => void;
-  readonly __wbindgen_start: () => void;
 }
 
 /**
@@ -38,9 +23,8 @@ export interface InitOutput {
 * for everything else, calls `WebAssembly.instantiate` directly.
 *
 * @param {InitInput | Promise<InitInput>} module_or_path
-* @param {WebAssembly.Memory} maybe_memory
 *
 * @returns {Promise<InitOutput>}
 */
-export default function init (module_or_path?: InitInput | Promise<InitInput>, maybe_memory: WebAssembly.Memory): Promise<InitOutput>;
+export default function init (module_or_path?: InitInput | Promise<InitInput>): Promise<InitOutput>;
         
\ No newline at end of file
diff --git a/codecs/oxipng/pkg/squoosh_oxipng.js b/codecs/oxipng/pkg/squoosh_oxipng.js
index 53d14fc9..45afd16e 100644
--- a/codecs/oxipng/pkg/squoosh_oxipng.js
+++ b/codecs/oxipng/pkg/squoosh_oxipng.js
@@ -1,21 +1,5 @@
 
 let wasm;
-let memory;
-
-const heap = new Array(32).fill(undefined);
-
-heap.push(undefined, null, true, false);
-
-let heap_next = heap.length;
-
-function addHeapObject(obj) {
-    if (heap_next === heap.length) heap.push(heap.length + 1);
-    const idx = heap_next;
-    heap_next = heap[idx];
-
-    heap[idx] = obj;
-    return idx;
-}
 
 let cachedTextDecoder = new TextDecoder('utf-8', { ignoreBOM: true, fatal: true });
 
@@ -23,48 +7,14 @@ cachedTextDecoder.decode();
 
 let cachegetUint8Memory0 = null;
 function getUint8Memory0() {
-    if (cachegetUint8Memory0 === null || cachegetUint8Memory0.buffer !== wasm.__wbindgen_export_0.buffer) {
-        cachegetUint8Memory0 = new Uint8Array(wasm.__wbindgen_export_0.buffer);
+    if (cachegetUint8Memory0 === null || cachegetUint8Memory0.buffer !== wasm.memory.buffer) {
+        cachegetUint8Memory0 = new Uint8Array(wasm.memory.buffer);
     }
     return cachegetUint8Memory0;
 }
 
 function getStringFromWasm0(ptr, len) {
-    return cachedTextDecoder.decode(getUint8Memory0().slice(ptr, ptr + len));
-}
-
-function getObject(idx) { return heap[idx]; }
-
-function dropObject(idx) {
-    if (idx < 36) return;
-    heap[idx] = heap_next;
-    heap_next = idx;
-}
-
-function takeObject(idx) {
-    const ret = getObject(idx);
-    dropObject(idx);
-    return ret;
-}
-/**
-* @returns {any}
-*/
-export function worker_initializer() {
-    var ret = wasm.worker_initializer();
-    return takeObject(ret);
-}
-
-/**
-* @param {number} num
-*/
-export function start_main_thread(num) {
-    wasm.start_main_thread(num);
-}
-
-/**
-*/
-export function start_worker_thread() {
-    wasm.start_worker_thread();
+    return cachedTextDecoder.decode(getUint8Memory0().subarray(ptr, ptr + len));
 }
 
 let WASM_VECTOR_LEN = 0;
@@ -78,8 +28,8 @@ function passArray8ToWasm0(arg, malloc) {
 
 let cachegetInt32Memory0 = null;
 function getInt32Memory0() {
-    if (cachegetInt32Memory0 === null || cachegetInt32Memory0.buffer !== wasm.__wbindgen_export_0.buffer) {
-        cachegetInt32Memory0 = new Int32Array(wasm.__wbindgen_export_0.buffer);
+    if (cachegetInt32Memory0 === null || cachegetInt32Memory0.buffer !== wasm.memory.buffer) {
+        cachegetInt32Memory0 = new Int32Array(wasm.memory.buffer);
     }
     return cachegetInt32Memory0;
 }
@@ -93,25 +43,19 @@ function getArrayU8FromWasm0(ptr, len) {
 * @returns {Uint8Array}
 */
 export function optimise(data, level) {
-    try {
-        const retptr = wasm.__wbindgen_export_1.value - 16;
-        wasm.__wbindgen_export_1.value = retptr;
-        var ptr0 = passArray8ToWasm0(data, wasm.__wbindgen_malloc);
-        var len0 = WASM_VECTOR_LEN;
-        wasm.optimise(retptr, ptr0, len0, level);
-        var r0 = getInt32Memory0()[retptr / 4 + 0];
-        var r1 = getInt32Memory0()[retptr / 4 + 1];
-        var v1 = getArrayU8FromWasm0(r0, r1).slice();
-        wasm.__wbindgen_free(r0, r1 * 1);
-        return v1;
-    } finally {
-        wasm.__wbindgen_export_1.value += 16;
-    }
+    var ptr0 = passArray8ToWasm0(data, wasm.__wbindgen_malloc);
+    var len0 = WASM_VECTOR_LEN;
+    wasm.optimise(8, ptr0, len0, level);
+    var r0 = getInt32Memory0()[8 / 4 + 0];
+    var r1 = getInt32Memory0()[8 / 4 + 1];
+    var v1 = getArrayU8FromWasm0(r0, r1).slice();
+    wasm.__wbindgen_free(r0, r1 * 1);
+    return v1;
 }
 
-async function load(module, imports, maybe_memory) {
+async function load(module, imports) {
     if (typeof Response === 'function' && module instanceof Response) {
-        memory = imports.wbg.memory = new WebAssembly.Memory({initial:17,maximum:16384,shared:true});
+
         if (typeof WebAssembly.instantiateStreaming === 'function') {
             try {
                 return await WebAssembly.instantiateStreaming(module, imports);
@@ -130,7 +74,7 @@ async function load(module, imports, maybe_memory) {
         return await WebAssembly.instantiate(bytes, imports);
 
     } else {
-        memory = imports.wbg.memory = maybe_memory;
+
         const instance = await WebAssembly.instantiate(module, imports);
 
         if (instance instanceof WebAssembly.Instance) {
@@ -142,24 +86,12 @@ async function load(module, imports, maybe_memory) {
     }
 }
 
-async function init(input, maybe_memory) {
+async function init(input) {
     if (typeof input === 'undefined') {
         input = import.meta.url.replace(/\.js$/, '_bg.wasm');
     }
     const imports = {};
     imports.wbg = {};
-    imports.wbg.__wbindgen_module = function() {
-        var ret = init.__wbindgen_wasm_module;
-        return addHeapObject(ret);
-    };
-    imports.wbg.__wbindgen_memory = function() {
-        var ret = wasm.__wbindgen_export_0;
-        return addHeapObject(ret);
-    };
-    imports.wbg.__wbg_of_6510501edc06d65e = function(arg0, arg1) {
-        var ret = Array.of(takeObject(arg0), takeObject(arg1));
-        return addHeapObject(ret);
-    };
     imports.wbg.__wbindgen_throw = function(arg0, arg1) {
         throw new Error(getStringFromWasm0(arg0, arg1));
     };
@@ -168,11 +100,11 @@ async function init(input, maybe_memory) {
         input = fetch(input);
     }
 
-    const { instance, module } = await load(await input, imports, maybe_memory);
+    const { instance, module } = await load(await input, imports);
 
     wasm = instance.exports;
     init.__wbindgen_wasm_module = module;
-    wasm.__wbindgen_start();
+
     return wasm;
 }
 
diff --git a/codecs/oxipng/pkg/squoosh_oxipng_bg.wasm.d.ts b/codecs/oxipng/pkg/squoosh_oxipng_bg.wasm.d.ts
index 832b7200..81b35d76 100644
--- a/codecs/oxipng/pkg/squoosh_oxipng_bg.wasm.d.ts
+++ b/codecs/oxipng/pkg/squoosh_oxipng_bg.wasm.d.ts
@@ -1,12 +1,8 @@
 /* tslint:disable */
 /* eslint-disable */
-export function worker_initializer(): number;
-export function start_main_thread(a: number): void;
-export function start_worker_thread(): void;
+export const memory: WebAssembly.Memory;
 export function optimise(a: number, b: number, c: number, d: number): void;
 export function malloc(a: number): number;
 export function free(a: number): void;
-export const __wbindgen_export_0: WebAssembly.Memory;
 export function __wbindgen_malloc(a: number): number;
 export function __wbindgen_free(a: number, b: number): void;
-export function __wbindgen_start(): void;
diff --git a/codecs/oxipng/rust-toolchain b/codecs/oxipng/rust-toolchain
new file mode 100644
index 00000000..bf867e0a
--- /dev/null
+++ b/codecs/oxipng/rust-toolchain
@@ -0,0 +1 @@
+nightly
diff --git a/codecs/oxipng/spawn.js b/codecs/oxipng/spawn.js
deleted file mode 100644
index 5bcaa96e..00000000
--- a/codecs/oxipng/spawn.js
+++ /dev/null
@@ -1,23 +0,0 @@
-import initOxiPNG, { worker_initializer, start_main_thread, optimise } from './pkg/oxipng.js';
-import wasmUrl from "./pkg/oxipng_bg.wasm";
-
-async function startMainThread() {
-  let num = navigator.hardwareConcurrency;
-  await initOxiPNG(fetch(wasmUrl));
-  let workerInit = worker_initializer();
-  let workers = [];
-  for (let i = 0; i < num; i++) {
-    workers.push(new Promise(resolve => {
-      let worker = new Worker("./worker.js", { type: "module" });
-      worker.postMessage(workerInit);
-      worker.addEventListener('message', resolve, { once: true });
-    }));
-  }
-  await Promise.all(workers);
-  start_main_thread(num);
-  return {
-    optimise
-  };
-}
-
-export default startMainThread();
diff --git a/codecs/oxipng/spawn.ts b/codecs/oxipng/spawn.ts
new file mode 100644
index 00000000..5b1c15cf
--- /dev/null
+++ b/codecs/oxipng/spawn.ts
@@ -0,0 +1,28 @@
+import initOxiPNG, {
+  worker_initializer,
+  start_main_thread,
+  optimise,
+} from './pkg-parallel';
+import wasmUrl from './pkg-parallel/oxipng_bg.wasm';
+import { WorkerInit } from './worker';
+
+function initWorker(worker: Worker, workerInit: WorkerInit) {
+  return new Promise((resolve) => {
+    worker.postMessage(workerInit);
+    worker.addEventListener('message', () => resolve(), { once: true });
+  });
+}
+
+async function startMainThread() {
+  const num = navigator.hardwareConcurrency;
+  const workers = Array.from({ length: num }, () => new Worker('./worker', { type: 'module' }));
+  await initOxiPNG(fetch(wasmUrl), undefined as any);
+  const workerInit: WorkerInit = worker_initializer();
+  await Promise.all(workers.map(worker => initWorker(worker, workerInit)));
+  start_main_thread(num);
+  return {
+    optimise,
+  };
+}
+
+export default startMainThread();
diff --git a/codecs/oxipng/src/lib.rs b/codecs/oxipng/src/lib.rs
index a494604e..9b40254c 100644
--- a/codecs/oxipng/src/lib.rs
+++ b/codecs/oxipng/src/lib.rs
@@ -1,47 +1,11 @@
+use wasm_bindgen::prelude::*;
+
 mod malloc_shim;
 
-use crossbeam_deque::Injector;
-use once_cell::sync::OnceCell;
-use wasm_bindgen::prelude::*;
-use wasm_bindgen::JsValue;
-use oxipng::AlphaOptim;
+#[cfg(feature = "parallel")]
+pub mod parallel;
 
 #[wasm_bindgen]
-extern "C" {
-    #[wasm_bindgen(js_namespace = Array, js_name = of)]
-    fn array_of_2(a: JsValue, b: JsValue) -> JsValue;
-}
-
-static TASKS: OnceCell<Injector<rayon::ThreadBuilder>> = OnceCell::new();
-
-#[wasm_bindgen]
-pub fn worker_initializer() -> JsValue {
-    TASKS.get_or_init(Injector::new);
-    array_of_2(wasm_bindgen::module(), wasm_bindgen::memory())
-}
-
-#[wasm_bindgen]
-pub fn start_main_thread(num: usize) {
-    let tasks = TASKS.get().unwrap();
-
-    rayon::ThreadPoolBuilder::new()
-        .num_threads(num)
-        .spawn_handler(|thread| Ok(tasks.push(thread)))
-        .build_global()
-        .unwrap_throw()
-}
-
-#[wasm_bindgen]
-pub fn start_worker_thread() {
-    let tasks = TASKS.get().unwrap();
-    loop {
-        if let crossbeam_deque::Steal::Success(task) = tasks.steal() {
-            return task.run();
-        }
-    }
-}
-
-#[wasm_bindgen(catch)]
 pub fn optimise(data: &[u8], level: u8) -> Vec<u8> {
   let mut options = oxipng::Options::from_preset(level);
   options.alphas.insert(AlphaOptim::Black);
diff --git a/codecs/oxipng/src/parallel.rs b/codecs/oxipng/src/parallel.rs
new file mode 100644
index 00000000..8354f78e
--- /dev/null
+++ b/codecs/oxipng/src/parallel.rs
@@ -0,0 +1,39 @@
+use crossbeam_deque::Injector;
+use once_cell::sync::OnceCell;
+use wasm_bindgen::prelude::*;
+use wasm_bindgen::JsValue;
+
+#[wasm_bindgen]
+extern "C" {
+    #[wasm_bindgen(js_namespace = Array, js_name = of)]
+    fn array_of_2(a: JsValue, b: JsValue) -> JsValue;
+}
+
+static TASKS: OnceCell<Injector<rayon::ThreadBuilder>> = OnceCell::new();
+
+#[wasm_bindgen]
+pub fn worker_initializer() -> JsValue {
+    TASKS.get_or_init(Injector::new);
+    array_of_2(wasm_bindgen::module(), wasm_bindgen::memory())
+}
+
+#[wasm_bindgen]
+pub fn start_main_thread(num: usize) {
+    let tasks = TASKS.get().unwrap();
+
+    rayon::ThreadPoolBuilder::new()
+        .num_threads(num)
+        .spawn_handler(|thread| Ok(tasks.push(thread)))
+        .build_global()
+        .unwrap_throw()
+}
+
+#[wasm_bindgen]
+pub fn start_worker_thread() {
+    let tasks = TASKS.get().unwrap();
+    loop {
+        if let crossbeam_deque::Steal::Success(task) = tasks.steal() {
+            return task.run();
+        }
+    }
+}
diff --git a/codecs/oxipng/worker.js b/codecs/oxipng/worker.js
deleted file mode 100644
index 0778cdff..00000000
--- a/codecs/oxipng/worker.js
+++ /dev/null
@@ -1,7 +0,0 @@
-import initOxiPNG, { start_worker_thread } from './pkg/squoosh_oxipng.js';
-
-addEventListener('message', async ({ data: [module, memory] }) => {
-  postMessage(null);
-  await initOxiPNG(module, memory);
-  start_worker_thread();
-}, { once: true });
diff --git a/codecs/oxipng/worker.ts b/codecs/oxipng/worker.ts
new file mode 100644
index 00000000..9a08f4c9
--- /dev/null
+++ b/codecs/oxipng/worker.ts
@@ -0,0 +1,20 @@
+/// <reference lib="webworker" />
+
+import initOxiPNG, { start_worker_thread } from './pkg-parallel';
+
+export type WorkerInit = [WebAssembly.Module, WebAssembly.Memory];
+
+addEventListener(
+  'message',
+  async (event) => {
+    // Tell the "main" thread that we've received the message.
+    //
+    // At this point, the "main" thread can run Wasm that
+    // will synchronously block waiting on other atomics.
+    postMessage(null);
+
+    await initOxiPNG(...(event.data as WorkerInit));
+    start_worker_thread();
+  },
+  { once: true },
+);
diff --git a/src/codecs/oxipng/encoder.ts b/src/codecs/oxipng/encoder.ts
index 69b17091..4af107b9 100644
--- a/src/codecs/oxipng/encoder.ts
+++ b/src/codecs/oxipng/encoder.ts
@@ -1,5 +1,5 @@
 // @ts-ignore
-import optimiser from '../../../codecs/oxipng/spawn.js';
+import optimiser from '../../../codecs/oxipng/spawn';
 import { EncodeOptions } from './encoder-meta';
 
 export async function compress(data: ArrayBuffer, options: EncodeOptions): Promise<ArrayBuffer> {