diff --git a/scripts/runner.node.mjs b/scripts/runner.node.mjs
index fd9aee180b..cdf824ddfb 100755
--- a/scripts/runner.node.mjs
+++ b/scripts/runner.node.mjs
@@ -80,6 +80,7 @@ function getNodeParallelTestTimeout(testPath) {
   if (testPath.includes("test-dns")) {
     return 90_000;
   }
+  if (!isCI) return 60_000; // everything slower in debug mode
   return 20_000;
 }
 
@@ -449,7 +450,7 @@ async function runTests() {
 
       if (parallelism > 1) {
         console.log(grouptitle);
-        result = await fn();
+        result = await fn(index);
       } else {
         result = await startGroup(grouptitle, fn);
       }
@@ -469,6 +470,7 @@ async function runTests() {
       const label = `${getAnsi(color)}[${index}/${total}] ${title} - ${error}${getAnsi("reset")}`;
       startGroup(label, () => {
         if (parallelism > 1) return;
+        if (!isCI) return;
         process.stderr.write(stdoutPreview);
       });
 
@@ -671,7 +673,9 @@ async function runTests() {
         const title = join(relative(cwd, vendorPath), testPath).replace(/\\/g, "/");
 
         if (testRunner === "bun") {
-          await runTest(title, () => spawnBunTest(execPath, testPath, { cwd: vendorPath }));
+          await runTest(title, index =>
+            spawnBunTest(execPath, testPath, { cwd: vendorPath, env: { TEST_SERIAL_ID: index } }),
+          );
         } else {
           const testRunnerPath = join(cwd, "test", "runners", `${testRunner}.ts`);
           if (!existsSync(testRunnerPath)) {
@@ -1298,6 +1302,7 @@ async function spawnBun(execPath, { args, cwd, timeout, env, stdout, stderr }) {
  * @param {object} [opts]
  * @param {string} [opts.cwd]
  * @param {string[]} [opts.args]
+ * @param {object} [opts.env]
  * @returns {Promise<TestResult>}
  */
 async function spawnBunTest(execPath, testPath, opts = { cwd }) {
@@ -1331,6 +1336,7 @@ async function spawnBunTest(execPath, testPath, opts = { cwd }) {
 
   const env = {
     GITHUB_ACTIONS: "true", // always true so annotations are parsed
+    ...opts["env"],
   };
   if ((basename(execPath).includes("asan") || !isCI) && shouldValidateExceptions(relative(cwd, absPath))) {
     env.BUN_JSC_validateExceptionChecks = "1";