diff --git a/packages/SwingSet/src/kernel/vatManager/subprocessSupervisor.js b/packages/SwingSet/src/kernel/vatManager/subprocessSupervisor.js
index 5ed4a2dd7a3..a3247d24481 100644
--- a/packages/SwingSet/src/kernel/vatManager/subprocessSupervisor.js
+++ b/packages/SwingSet/src/kernel/vatManager/subprocessSupervisor.js
@@ -3,11 +3,15 @@ import '@agoric/install-ses';
 
 import anylogger from 'anylogger';
 import fs from 'fs';
-import Netstring from 'netstring-stream';
 
 import { assert } from '@agoric/assert';
 import { importBundle } from '@agoric/import-bundle';
 import { Remotable, getInterfaceOf, makeMarshal } from '@agoric/marshal';
+import { arrayEncoderStream, arrayDecoderStream } from '../../worker-protocol';
+import {
+  netstringEncoderStream,
+  netstringDecoderStream,
+} from '../../netstring';
 import { waitUntilQuiescent } from '../../waitUntilQuiescent';
 import { makeLiveSlots } from '../liveSlots';
 
@@ -71,17 +75,19 @@ function doNotify(vpid, vp) {
   }
 }
 
-const toParent = Netstring.writeStream();
-toParent.pipe(fs.createWriteStream('IGNORED', { fd: 4, encoding: 'utf-8' }));
+const toParent = arrayEncoderStream();
+toParent
+  .pipe(netstringEncoderStream())
+  .pipe(fs.createWriteStream('IGNORED', { fd: 4, encoding: 'utf-8' }));
 
 const fromParent = fs
   .createReadStream('IGNORED', { fd: 3, encoding: 'utf-8' })
-  .pipe(Netstring.readStream());
-fromParent.setEncoding('utf-8');
+  .pipe(netstringDecoderStream())
+  .pipe(arrayDecoderStream());
 
 function sendUplink(msg) {
   assert(msg instanceof Array, `msg must be an Array`);
-  toParent.write(JSON.stringify(msg));
+  toParent.write(msg);
 }
 
 // fromParent.on('data', data => {
@@ -90,7 +96,7 @@ function sendUplink(msg) {
 // });
 
 fromParent.on('data', data => {
-  const [type, ...margs] = JSON.parse(data);
+  const [type, ...margs] = data;
   workerLog(`received`, type);
   if (type === 'start') {
     // TODO: parent should send ['start', vatID]
diff --git a/packages/SwingSet/src/kernel/vatManager/worker-subprocess-node.js b/packages/SwingSet/src/kernel/vatManager/worker-subprocess-node.js
index d5d1bfc466a..7c4f45db8c4 100644
--- a/packages/SwingSet/src/kernel/vatManager/worker-subprocess-node.js
+++ b/packages/SwingSet/src/kernel/vatManager/worker-subprocess-node.js
@@ -75,8 +75,8 @@ export function makeNodeSubprocessFactory(tools) {
     const { fromChild, toChild, terminate, done } = startSubprocessWorker();
 
     function sendToWorker(msg) {
-      assert(msg instanceof Array);
-      toChild.write(JSON.stringify(msg));
+      assert(Array.isArray(msg));
+      toChild.write(msg);
     }
 
     const {
@@ -114,10 +114,7 @@ export function makeNodeSubprocessFactory(tools) {
       }
     }
 
-    fromChild.on('data', data => {
-      const msg = JSON.parse(data);
-      handleUpstream(msg);
-    });
+    fromChild.on('data', handleUpstream);
 
     parentLog(`instructing worker to load bundle..`);
     sendToWorker(['setBundle', bundle, vatParameters]);
diff --git a/packages/SwingSet/src/spawnSubprocessWorker.js b/packages/SwingSet/src/spawnSubprocessWorker.js
index e02008d6225..355e44d4e9c 100644
--- a/packages/SwingSet/src/spawnSubprocessWorker.js
+++ b/packages/SwingSet/src/spawnSubprocessWorker.js
@@ -1,8 +1,13 @@
 // this file is loaded by the controller, in the start compartment
 import { spawn } from 'child_process';
-import Netstring from 'netstring-stream';
-
 import { makePromiseKit } from '@agoric/promise-kit';
+import { arrayEncoderStream, arrayDecoderStream } from './worker-protocol';
+import { netstringEncoderStream, netstringDecoderStream } from './netstring';
+
+// Start a subprocess from a given executable, and arrange a bidirectional
+// message channel with a "supervisor" within that process. Return a {
+// toChild, fromChild } pair of Streams which accept/emit hardened Arrays of
+// JSON-serializable data.
 
 // eslint-disable-next-line no-unused-vars
 function parentLog(first, ...args) {
@@ -18,11 +23,12 @@ const stdio = harden(['inherit', 'inherit', 'inherit', 'pipe', 'pipe']);
 export function startSubprocessWorker(execPath, procArgs = []) {
   const proc = spawn(execPath, procArgs, { stdio });
 
-  const toChild = Netstring.writeStream();
-  toChild.pipe(proc.stdio[3]);
+  const toChild = arrayEncoderStream();
+  toChild.pipe(netstringEncoderStream()).pipe(proc.stdio[3]);
   // proc.stdio[4].setEncoding('utf-8');
-  const fromChild = proc.stdio[4].pipe(Netstring.readStream());
-  fromChild.setEncoding('utf-8');
+  const fromChild = proc.stdio[4]
+    .pipe(netstringDecoderStream())
+    .pipe(arrayDecoderStream());
 
   // fromChild.addListener('data', data => parentLog(`fd4 data`, data));
   // toChild.write('hello child');
@@ -43,13 +49,13 @@ export function startSubprocessWorker(execPath, procArgs = []) {
     proc.kill();
   }
 
-  // the Netstring objects don't like being hardened, so we wrap the methods
+  // the Transform objects don't like being hardened, so we wrap the methods
   // that get used
   const wrappedFromChild = {
-    on: (evName, f) => fromChild.on(evName, f),
+    on: (...args) => fromChild.on(...args),
   };
   const wrappedToChild = {
-    write: data => toChild.write(data),
+    write: (...args) => toChild.write(...args),
   };
 
   return harden({