diff --git a/src/cli.ts b/src/cli.ts
index 46c549b..84efda7 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -1,4 +1,5 @@
 #!/usr/bin/env node
+import shellquote from 'shell-quote'
 import { Command } from 'commander'
 import { SandboxManager } from './index.js'
 import type { SandboxRuntimeConfig } from './sandbox/sandbox-config.js'
@@ -147,8 +148,11 @@ async function main(): Promise<void> {
             command = options.c
             logForDebugging(`Command string mode (-c): ${command}`)
           } else if (commandArgs.length > 0) {
-            // Default mode: simple join
-            command = commandArgs.join(' ')
+            // Default mode: argv-style invocation. The result is later
+            // executed via `bash -c <command>`, so each arg must be
+            // shell-quoted to survive that re-parse — a plain join(' ')
+            // splits arguments containing whitespace (#157).
+            command = shellquote.quote(commandArgs)
             logForDebugging(`Original command: ${command}`)
           } else {
             console.error(
diff --git a/test/cli.test.ts b/test/cli.test.ts
index 2e9f74a..2671add 100644
--- a/test/cli.test.ts
+++ b/test/cli.test.ts
@@ -98,6 +98,24 @@ describe('CLI', () => {
       expect(result.stdout).toBe('no newline')
       expect(result.status).toBe(0)
     })
+
+    test('preserves argument boundaries when args contain spaces', () => {
+      // Regression for #157: positional args are later run via `bash -c`,
+      // so they must be shell-quoted. printf '%s\n' emits one line per
+      // arg, which exposes whether "hello world" arrived as one token
+      // (correct) or was re-split into "hello" and "world".
+      const result = runCli(['printf', '%s\n', 'hello world', 'a b'])
+      expect(result.stdout).toBe('hello world\na b\n')
+      expect(result.status).toBe(0)
+    })
+
+    test('preserves shell metacharacters in positional args', () => {
+      // Positional mode is argv-style; metacharacters in an arg are data,
+      // not shell syntax (use -c for shell semantics).
+      const result = runCli(['printf', '%s', '$HOME;|&'])
+      expect(result.stdout).toBe('$HOME;|&')
+      expect(result.status).toBe(0)
+    })
   })
 
   describe('error handling', () => {