diff --git a/scripts/test-parallel-utils.mjs b/scripts/test-parallel-utils.mjs
new file mode 100644
index 00000000000..96bf86a3c34
--- /dev/null
+++ b/scripts/test-parallel-utils.mjs
@@ -0,0 +1,35 @@
+const DEFAULT_OUTPUT_CAPTURE_LIMIT = 200_000;
+
+const fatalOutputPatterns = [
+  /FATAL ERROR:.*heap out of memory/i,
+  /Allocation failed - JavaScript heap out of memory/i,
+  /node::OOMErrorHandler/i,
+];
+
+export function appendCapturedOutput(current, chunk, limit = DEFAULT_OUTPUT_CAPTURE_LIMIT) {
+  if (!chunk) {
+    return current;
+  }
+  const next = `${current}${chunk}`;
+  if (next.length <= limit) {
+    return next;
+  }
+  return next.slice(-limit);
+}
+
+export function hasFatalTestRunOutput(output) {
+  return fatalOutputPatterns.some((pattern) => pattern.test(output));
+}
+
+export function resolveTestRunExitCode({ code, signal, output }) {
+  if (typeof code === "number" && code !== 0) {
+    return code;
+  }
+  if (signal) {
+    return 1;
+  }
+  if (hasFatalTestRunOutput(output)) {
+    return 1;
+  }
+  return code ?? 0;
+}
diff --git a/scripts/test-parallel.mjs b/scripts/test-parallel.mjs
index 1a128cf70dd..9571668f3ba 100644
--- a/scripts/test-parallel.mjs
+++ b/scripts/test-parallel.mjs
@@ -4,6 +4,7 @@ import os from "node:os";
 import path from "node:path";
 import { channelTestPrefixes } from "../vitest.channel-paths.mjs";
 import { isUnitConfigTestFile } from "../vitest.unit-paths.mjs";
+import { appendCapturedOutput, resolveTestRunExitCode } from "./test-parallel-utils.mjs";
 import {
   loadTestRunnerBehavior,
   loadUnitTimingManifest,
@@ -740,10 +741,11 @@ const runOnce = (entry, extraArgs = []) =>
     const resolvedNodeOptions = heapFlag
       ? `${nextNodeOptions} ${heapFlag}`.trim()
       : nextNodeOptions;
+    let output = "";
     let child;
     try {
       child = spawn(pnpm, args, {
-        stdio: "inherit",
+        stdio: ["inherit", "pipe", "pipe"],
         env: { ...process.env, VITEST_GROUP: entry.name, NODE_OPTIONS: resolvedNodeOptions },
         shell: isWindows,
       });
@@ -753,17 +755,26 @@ const runOnce = (entry, extraArgs = []) =>
       return;
     }
     children.add(child);
+    child.stdout?.on("data", (chunk) => {
+      const text = chunk.toString();
+      output = appendCapturedOutput(output, text);
+      process.stdout.write(chunk);
+    });
+    child.stderr?.on("data", (chunk) => {
+      const text = chunk.toString();
+      output = appendCapturedOutput(output, text);
+      process.stderr.write(chunk);
+    });
     child.on("error", (err) => {
       console.error(`[test-parallel] child error: ${String(err)}`);
     });
-    child.on("exit", (code, signal) => {
+    child.on("close", (code, signal) => {
       children.delete(child);
+      const resolvedCode = resolveTestRunExitCode({ code, signal, output });
       console.log(
-        `[test-parallel] done ${entry.name} code=${String(code ?? (signal ? 1 : 0))} elapsed=${formatElapsedMs(
-          Date.now() - startedAt,
-        )}`,
+        `[test-parallel] done ${entry.name} code=${String(resolvedCode)} elapsed=${formatElapsedMs(Date.now() - startedAt)}`,
       );
-      resolve(code ?? (signal ? 1 : 0));
+      resolve(resolvedCode);
     });
   });
 
diff --git a/test/scripts/test-parallel.test.ts b/test/scripts/test-parallel.test.ts
new file mode 100644
index 00000000000..d5826de5412
--- /dev/null
+++ b/test/scripts/test-parallel.test.ts
@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import {
+  appendCapturedOutput,
+  hasFatalTestRunOutput,
+  resolveTestRunExitCode,
+} from "../../scripts/test-parallel-utils.mjs";
+
+describe("scripts/test-parallel fatal output guard", () => {
+  it("fails a zero exit when V8 reports an out-of-memory fatal", () => {
+    const output = [
+      "FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory",
+      "node::OOMErrorHandler(char const*, v8::OOMDetails const&)",
+      "[test-parallel] done unit-fast code=0 elapsed=210.9s",
+    ].join("\n");
+
+    expect(hasFatalTestRunOutput(output)).toBe(true);
+    expect(resolveTestRunExitCode({ code: 0, signal: null, output })).toBe(1);
+  });
+
+  it("keeps a clean zero exit green", () => {
+    expect(
+      resolveTestRunExitCode({
+        code: 0,
+        signal: null,
+        output: "Test Files  3 passed (3)",
+      }),
+    ).toBe(0);
+  });
+
+  it("preserves explicit non-zero exits", () => {
+    expect(resolveTestRunExitCode({ code: 2, signal: null, output: "" })).toBe(2);
+  });
+
+  it("keeps only the tail of captured output", () => {
+    const output = appendCapturedOutput("", "abc", 5);
+    expect(appendCapturedOutput(output, "defg", 5)).toBe("cdefg");
+  });
+});