diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index 911a700d68d..9994ac12ecf 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -4,21 +4,19 @@ const {
   ArrayPrototypeFilter,
   ArrayPrototypeIncludes,
   ArrayPrototypeJoin,
-  ArrayPrototypePop,
   ArrayPrototypePush,
   ArrayPrototypeSlice,
   ArrayPrototypeSort,
   ObjectAssign,
   PromisePrototypeThen,
-  RegExpPrototypeSymbolSplit,
   SafePromiseAll,
   SafeSet,
-  StringPrototypeEndsWith,
 } = 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 console = require('internal/console/global');
 const {
   codes: {
@@ -114,28 +112,6 @@ 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) => {
@@ -151,9 +127,18 @@ 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 }),