diff --git a/packages/SwingSet/src/controller.js b/packages/SwingSet/src/controller.js
index 1691abcea2c..cc67db0eb3f 100644
--- a/packages/SwingSet/src/controller.js
+++ b/packages/SwingSet/src/controller.js
@@ -16,7 +16,7 @@ import { importBundle } from '@agoric/import-bundle';
 import { initSwingStore } from '@agoric/swing-store-simple';
 import { makeMeteringTransformer } from '@agoric/transform-metering';
 import { makeTransform } from '@agoric/transform-eventual-send';
-import { xsWorkerBin } from '@agoric/xs-vat-worker';
+import { locateWorkerBin } from '@agoric/xs-vat-worker';
 
 import { startSubprocessWorker } from './spawnSubprocessWorker';
 import { assertKnownOptions } from './assertOptions';
@@ -322,7 +322,8 @@ export async function buildVatController(
     // console.log(`--slog ${JSON.stringify(obj)}`);
   }
 
-  const startXsWorker = xsWorkerBin
+  const xsWorkerBin = locateWorkerBin({ resolve: path.resolve });
+  const startXsWorker = fs.existsSync(xsWorkerBin)
     ? () => startSubprocessWorker(xsWorkerBin, [])
     : undefined;
 
diff --git a/packages/SwingSet/test/workers/test-worker.js b/packages/SwingSet/test/workers/test-worker.js
index 4d877490b72..84a82ecf30b 100644
--- a/packages/SwingSet/test/workers/test-worker.js
+++ b/packages/SwingSet/test/workers/test-worker.js
@@ -1,11 +1,14 @@
 import '@agoric/install-ses';
 import test from 'ava';
-import { xsWorkerBin } from '@agoric/xs-vat-worker/src/locate';
+import { resolve } from 'path';
+import { existsSync } from 'fs';
+import { locateWorkerBin } from '@agoric/xs-vat-worker';
 import { loadBasedir, buildVatController } from '../../src/index';
 
 test('xs vat manager', async t => {
-  if (!xsWorkerBin) {
-    console.warn('XS vat worker not built; skipping');
+  const bin = locateWorkerBin({ resolve });
+  if (!existsSync(bin)) {
+    console.warn(`XS vat worker ${bin} not built; skipping`);
     t.falsy.skip(false);
     return;
   }
diff --git a/packages/xs-vat-worker/package.json b/packages/xs-vat-worker/package.json
index 736d505a961..d7f543b20ce 100644
--- a/packages/xs-vat-worker/package.json
+++ b/packages/xs-vat-worker/package.json
@@ -5,7 +5,6 @@
   "main": "src/locate.js",
   "module": "src/locate.js",
   "scripts": {
-    "postinstall": "cp src/locate-undefined.js src/locate.js",
     "build:xs-lin": "make -f xs-lin.mk",
     "test": "tape -r esm 'test/**/test-*.js'",
     "build": "exit 0",
diff --git a/packages/xs-vat-worker/src/locate-undefined.js b/packages/xs-vat-worker/src/locate-undefined.js
deleted file mode 100644
index 1ba903d1b52..00000000000
--- a/packages/xs-vat-worker/src/locate-undefined.js
+++ /dev/null
@@ -1 +0,0 @@
-export const xsWorkerBin = undefined;
diff --git a/packages/xs-vat-worker/src/locate.js b/packages/xs-vat-worker/src/locate.js
new file mode 100644
index 00000000000..4f946231069
--- /dev/null
+++ b/packages/xs-vat-worker/src/locate.js
@@ -0,0 +1,15 @@
+/**
+ * Locate the XS vat worker executable.
+ *
+ * Note: executable is not built by default.
+ * @see the `build:xs-lin` script in package.json
+ *
+ * @param {{ resolve: (...string) => string }} filesystem path access
+ * @returns { string } full path where linux debug executable is built;
+ *                     not guaranteed to exist.
+ */
+export function locateWorkerBin({ resolve }) {
+  const goal = 'debug'; // ISSUE: support, test release too?
+  const os = 'lin'; // ISSUE: support, test mac too?
+  return resolve(__dirname, '../build/bin', os, goal, 'xs-vat-worker');
+}
diff --git a/packages/xs-vat-worker/test/test-locate.js b/packages/xs-vat-worker/test/test-locate.js
index 82e7182b06b..a1769c80e37 100644
--- a/packages/xs-vat-worker/test/test-locate.js
+++ b/packages/xs-vat-worker/test/test-locate.js
@@ -1,8 +1,12 @@
+import { resolve } from 'path';
+
 import { test } from 'tape-promise/tape';
 
-import { xsWorkerBin } from '../src/locate';
+import { locateWorkerBin } from '../src/locate';
 
 test('locateWorkerBin', t => {
-  t.ok(!xsWorkerBin || xsWorkerBin.endsWith('xs-vat-worker'));
+  const bin = locateWorkerBin({ resolve });
+  t.ok(bin.startsWith('/'));
+  t.ok(bin.endsWith('/xs-vat-worker'));
   t.end();
 });
diff --git a/packages/xs-vat-worker/xs-lin.mk b/packages/xs-vat-worker/xs-lin.mk
index 6bc4f185896..9db23af4279 100644
--- a/packages/xs-vat-worker/xs-lin.mk
+++ b/packages/xs-vat-worker/xs-lin.mk
@@ -5,7 +5,6 @@ ROOT=$(PWD)/../..
 
 $(NODE_MODULES)/.bin/xs-vat-worker: build/bin/lin/debug/xs-vat-worker
 	cp $< $@
-	echo "export const xsWorkerBin =\n  '$@';" >src/locate.js
 
 build/bin/lin/debug/xs-vat-worker: build $(TOOLS)/mcconfig moddable/xs/platforms/lin_xs_cli.c compartmap.json manifest.json
 	ROOT=$(ROOT) PATH=$(TOOLS):$$PATH MODDABLE=$(MODDABLE) mcconfig -o build -p x-cli-lin -m -d