diff --git a/codecs/oxipng/spawn.ts b/codecs/oxipng/spawn.ts
index 59293615..14b1c1b4 100644
--- a/codecs/oxipng/spawn.ts
+++ b/codecs/oxipng/spawn.ts
@@ -54,7 +54,12 @@ async function startMainThread() {
 
   return {
     optimise,
+    freeWorkers: () => {
+      for (const worker of resolvedWorkers) {
+        worker.terminate();
+      }
+    },
   };
 }
 
-export default startMainThread();
+export default () => startMainThread();
diff --git a/src/codecs/oxipng/encoder.ts b/src/codecs/oxipng/encoder.ts
index ac54dd89..3232ea67 100644
--- a/src/codecs/oxipng/encoder.ts
+++ b/src/codecs/oxipng/encoder.ts
@@ -1,7 +1,12 @@
 // @ts-ignore
-import optimiser from '../../../codecs/oxipng';
+import init from '../../../codecs/oxipng/spawn';
 import { EncodeOptions } from './encoder-meta';
 
 export async function compress(data: ArrayBuffer, options: EncodeOptions): Promise<ArrayBuffer> {
-  return (await optimiser).optimise(new Uint8Array(data), options.level).buffer;
+  for (let i = 0; i < 100; i += 1) {
+    const optimiser = await init();
+    console.log(`Run #${i}: ${optimiser.optimise(new Uint8Array(data), options.level).buffer.byteLength} bytes`);
+    optimiser.freeWorkers();
+  }
+  return (await init()).optimise(new Uint8Array(data), options.level).buffer;
 }