diff --git a/src/packager.ts b/src/packager.ts
index ecad3b0..46ce880 100644
--- a/src/packager.ts
+++ b/src/packager.ts
@@ -2,7 +2,7 @@ import path, { join } from 'node:path';
 import { spawnSync } from 'node:child_process';
 import { existsSync, mkdirSync, rmSync, unlinkSync } from 'node:fs';
 import { readdir, mkdir } from 'node:fs/promises';
-import { toUrl, toUrlOrUndefined } from './util';
+import { createS3cmdArgs, toUrl, toUrlOrUndefined } from './util';
 import mv from 'mv';
 
 const DEFAULT_STAGING_DIR = '/tmp/data';
@@ -99,13 +99,11 @@ export async function download(
   if (source.protocol === 's3:') {
     const sourceFile = new URL(join(source.pathname, input.filename), source);
     const localFilename = join(stagingDir, input.filename);
-    const { status, stderr } = spawnSync('aws', [
-      's3',
-      endpointUrl ? `--endpoint-url=${endpointUrl}` : '',
-      'cp',
-      sourceFile.toString(),
-      localFilename
-    ]);
+    const args = createS3cmdArgs(
+      ['cp', sourceFile.toString(), localFilename],
+      endpointUrl
+    );
+    const { status, stderr } = spawnSync('aws', args);
     if (status !== 0) {
       if (stderr) {
         console.log(stderr.toString());
@@ -181,14 +179,11 @@ export async function uploadPackage(
   }
   if (dest.protocol === 's3:') {
     console.log(`Uploading package to ${dest.toString()}`);
-    const { status, stderr, error } = spawnSync('aws', [
-      's3',
-      s3EndpointUrl ? `--endpoint-url=${s3EndpointUrl}` : '',
-      'cp',
-      '--recursive',
-      stagingDir,
-      dest.toString()
-    ]);
+    const args = createS3cmdArgs(
+      ['cp', '--recursive', stagingDir, dest.toString()],
+      s3EndpointUrl
+    );
+    const { status, stderr, error } = spawnSync('aws', args);
     if (status !== 0) {
       if (error) {
         console.error(`Upload failed: ${error.message}`);
diff --git a/src/util.test.ts b/src/util.test.ts
new file mode 100644
index 0000000..b62dcfa
--- /dev/null
+++ b/src/util.test.ts
@@ -0,0 +1,13 @@
+import { createS3cmdArgs } from './util';
+
+describe('cmd args helper', () => {
+  test('can construct s3cmd args without s3 endpoint url', () => {
+    const args = createS3cmdArgs(['ls']);
+    expect(args).toEqual(['s3', 'ls']);
+  });
+
+  test('can construct s3cmd args s3 endpoint url', () => {
+    const args = createS3cmdArgs(['ls'], 'https://my.api.url.com');
+    expect(args).toEqual(['s3', '--endpoint-url=https://my.api.url.com', 'ls']);
+  });
+});
diff --git a/src/util.ts b/src/util.ts
index 6934d04..8c655e3 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -12,3 +12,14 @@ export function toUrl(url: string) {
     ? new URL(url)
     : new URL(`file://${path.resolve(url)}`);
 }
+
+export function createS3cmdArgs(
+  cmdArgs: string[],
+  s3EndpointUrl?: string
+): string[] {
+  const args = ['s3'];
+  if (s3EndpointUrl) {
+    args.push(`--endpoint-url=${s3EndpointUrl}`);
+  }
+  return args.concat(cmdArgs);
+}