diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index 5a40097..0091563 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -1,25 +1,23 @@
-// https://github.com/nodejs/node/blob/a165193c5c8e4bcfbd12b2c3f6e55a81a251c258/lib/internal/test_runner/runner.js
+// https://github.com/nodejs/node/blob/9825a7e01d35b9d49ebb58efed2c316012c19db6/lib/internal/test_runner/runner.js
 'use strict'
 const {
   ArrayFrom,
   ArrayPrototypeFilter,
   ArrayPrototypeIncludes,
   ArrayPrototypeJoin,
-  ArrayPrototypePop,
   ArrayPrototypePush,
   ArrayPrototypeSlice,
   ArrayPrototypeSort,
   ObjectAssign,
   PromisePrototypeThen,
-  RegExpPrototypeSymbolSplit,
   SafePromiseAll,
-  SafeSet,
-  StringPrototypeEndsWith
+  SafeSet
 } = require('#internal/per_context/primordials')
 
-const { Buffer } = require('buffer')
 const { spawn } = require('child_process')
 const { readdirSync, statSync } = require('fs')
+// TODO(aduh95): switch to internal/readline/interface when backporting to Node.js 16.x is no longer a concern.
+const { createInterface } = require('readline')
 const {
   codes: {
     ERR_TEST_FAILURE
@@ -116,29 +114,6 @@ function getRunArgs ({ path, inspectPort }) {
   return argv
 }
 
-function makeStderrCallback (callback) {
-  if (!isUsingInspector()) {
-    return callback
-  }
-  let buffer = Buffer.alloc(0)
-  return (data) => {
-    callback(data)
-    const newData = Buffer.concat([buffer, data])
-    const str = newData.toString('utf8')
-    let lines = str
-    if (StringPrototypeEndsWith(lines, '\n')) {
-      buffer = Buffer.alloc(0)
-    } else {
-      lines = RegExpPrototypeSymbolSplit(/\r?\n/, str)
-      buffer = Buffer.from(ArrayPrototypePop(lines), 'utf8')
-      lines = ArrayPrototypeJoin(lines, '\n')
-    }
-    if (isInspectorMessage(lines)) {
-      process.stderr.write(lines)
-    }
-  }
-}
-
 function runTestFile (path, root, inspectPort) {
   const subtest = root.createSubtest(Test, path, async (t) => {
     const args = getRunArgs({ path, inspectPort })
@@ -153,9 +128,18 @@ function runTestFile (path, root, inspectPort) {
       err = error
     })
 
-    child.stderr.on('data', makeStderrCallback((data) => {
+    child.stderr.on('data', (data) => {
       stderr += data
-    }))
+    })
+
+    if (isUsingInspector()) {
+      const rl = createInterface({ input: child.stderr })
+      rl.on('line', (line) => {
+        if (isInspectorMessage(line)) {
+          process.stderr.write(line + '\n')
+        }
+      })
+    }
 
     const { 0: { 0: code, 1: signal }, 1: stdout } = await SafePromiseAll([
       once(child, 'exit', { signal: t.signal }),