diff --git a/packages/SwingSet/src/controller.js b/packages/SwingSet/src/controller.js
index 482fdaf24d3..1c60578a1bc 100644
--- a/packages/SwingSet/src/controller.js
+++ b/packages/SwingSet/src/controller.js
@@ -125,6 +125,45 @@ export function loadBasedir(basedir) {
   return config;
 }
 
+function normalizeConfigDescriptor(desc, dirname, expectParameters) {
+  if (desc) {
+    for (const name of Object.keys(desc)) {
+      const entry = desc[name];
+      if (entry.sourcePath) {
+        entry.sourcePath = path.resolve(dirname, entry.sourcePath);
+      }
+      if (entry.bundlePath) {
+        entry.bundlePath = path.resolve(dirname, entry.bundlePath);
+      }
+      if (expectParameters && !entry.parameters) {
+        entry.parameters = {};
+      }
+    }
+  }
+}
+
+export function loadSwingsetConfigFile(configPath) {
+  try {
+    const config = JSON.parse(fs.readFileSync(configPath));
+    const dirname = path.dirname(configPath);
+    normalizeConfigDescriptor(config.vats, dirname, true);
+    normalizeConfigDescriptor(config.bundles, dirname, false);
+    // normalizeConfigDescriptor(config.devices, dirname, true); // TODO: represent devices
+    if (!config.bootstrap) {
+      throw Error(`no designated bootstrap vat in ${configPath}`);
+    } else if (!config.vats[config.bootstrap]) {
+      throw Error(`bootstrap vat ${config.bootstrap} not found in ${configPath}`);
+    }
+    return config;
+  } catch (e) {
+    if (e.code === 'ENOENT') {
+      return null;
+    } else {
+      throw e;
+    }
+  }
+}
+
 export async function buildVatController(
   config,
   argv = [],
diff --git a/packages/SwingSet/src/index.js b/packages/SwingSet/src/index.js
index fef3b160ec7..b71a668899b 100644
--- a/packages/SwingSet/src/index.js
+++ b/packages/SwingSet/src/index.js
@@ -1,4 +1,8 @@
-export { loadBasedir, buildVatController } from './controller';
+export {
+  loadBasedir,
+  loadSwingsetConfigFile,
+  buildVatController,
+} from './controller';
 
 export { buildMailboxStateMap, buildMailbox } from './devices/mailbox';
 export { buildTimer } from './devices/timer';
diff --git a/packages/swingset-runner/src/main.js b/packages/swingset-runner/src/main.js
index 376853627ce..e92b7e7de6a 100644
--- a/packages/swingset-runner/src/main.js
+++ b/packages/swingset-runner/src/main.js
@@ -5,7 +5,11 @@ import repl from 'repl';
 import util from 'util';
 
 import { makeStatLogger } from '@agoric/stat-logger';
-import { buildVatController, loadBasedir } from '@agoric/swingset-vat';
+import {
+  buildVatController,
+  loadSwingsetConfigFile,
+  loadBasedir,
+} from '@agoric/swingset-vat';
 import {
   initSwingStore as initSimpleSwingStore,
   openSwingStore as openSimpleSwingStore,
@@ -85,42 +89,6 @@ function fail(message, printUsage) {
   process.exit(1);
 }
 
-function normalizeConfigDescriptor(desc, dirname, expectParameters) {
-  if (desc) {
-    for (const name of Object.keys(desc)) {
-      const entry = desc[name];
-      if (entry.sourcePath) {
-        entry.sourcePath = path.resolve(dirname, entry.sourcePath);
-      }
-      if (entry.bundlePath) {
-        entry.bundlePath = path.resolve(dirname, entry.bundlePath);
-      }
-      if (expectParameters && !entry.parameters) {
-        entry.parameters = {};
-      }
-    }
-  }
-}
-
-function readConfig(configPath) {
-  try {
-    const config = JSON.parse(fs.readFileSync(configPath));
-    const dirname = path.dirname(configPath);
-    normalizeConfigDescriptor(config.vats, dirname, true);
-    normalizeConfigDescriptor(config.bundles, dirname, false);
-    // normalizeConfigDescriptor(config.devices, dirname, true); // TODO: represent devices
-    if (!config.bootstrap) {
-      fail(`no designated bootstrap vat in ${configPath}`);
-    } else if (!config.vats[config.bootstrap]) {
-      fail(`bootstrap vat ${config.bootstrap} not found in ${configPath}`);
-    }
-    return config;
-  } catch (e) {
-    fail(`bad config file: ${e}`);
-    return null; // just to make eslint shut up
-  }
-}
-
 function generateIndirectConfig(baseConfig) {
   const config = {
     bootstrap: 'launcher',
@@ -328,10 +296,13 @@ export async function main() {
 
   let config;
   if (configPath) {
-    config = readConfig(configPath);
+    config = loadSwingsetConfigFile(configPath);
+    if (config === null) {
+      fail(`config file ${configPath} not found`);
+    }
     basedir = path.dirname(configPath);
   } else {
-    config = await loadBasedir(basedir);
+    config = loadBasedir(basedir);
   }
   if (launchIndirectly) {
     config = generateIndirectConfig(config);