diff --git a/test/sequential/test-debugger-custom-port.js b/test/sequential/test-debugger-custom-port.js
index e6cee10ffa53b5..7c8abdc0c55174 100644
--- a/test/sequential/test-debugger-custom-port.js
+++ b/test/sequential/test-debugger-custom-port.js
@@ -9,22 +9,20 @@ const startCLI = require('../common/debugger');
 const assert = require('assert');
 
 // Custom port.
-{
-  const script = fixtures.path('debugger', 'three-lines.js');
+const script = fixtures.path('debugger', 'three-lines.js');
 
-  const cli = startCLI([`--port=${common.PORT}`, script]);
-
-  cli.waitForInitialBreak()
-    .then(() => cli.waitForPrompt())
-    .then(() => {
-      assert.match(cli.output, /debug>/, 'prints a prompt');
-      assert.match(
-        cli.output,
-        new RegExp(`< Debugger listening on [^\n]*${common.PORT}`),
-        'forwards child output');
-    })
-    .then(() => cli.quit())
-    .then((code) => {
-      assert.strictEqual(code, 0);
-    });
-}
+const cli = startCLI([`--port=${common.PORT}`, script]);
+(async function() {
+  try {
+    await cli.waitForInitialBreak();
+    await cli.waitForPrompt();
+    assert.match(cli.output, /debug>/, 'prints a prompt');
+    assert.match(
+      cli.output,
+      new RegExp(`< Debugger listening on [^\n]*${common.PORT}`),
+      'forwards child output');
+  } finally {
+    const code = await cli.quit();
+    assert.strictEqual(code, 0);
+  }
+})().then(common.mustCall());