diff --git a/packages/bun-types/bun.d.ts b/packages/bun-types/bun.d.ts
index d8c9402e2871..b9ca9d516c1e 100644
--- a/packages/bun-types/bun.d.ts
+++ b/packages/bun-types/bun.d.ts
@@ -8157,19 +8157,27 @@ declare module "bun" {
   type WritableSubprocess = Subprocess<"pipe", any, any>;
   /** Utility type for any process from {@link Bun.spawn()} with stdin, stdout, stderr all set to `"pipe"`. A combination of {@link ReadableSubprocess} and {@link WritableSubprocess} */
   type PipedSubprocess = Subprocess<"pipe", "pipe", "pipe">;
-  /** Utility type for any process from {@link Bun.spawn()} with stdin, stdout, stderr all set to `null` or similar. */
+  /**
+   * Utility type for any process from {@link Bun.spawn()} with stdin, stdout, stderr all set to `"ignore"`, `"inherit"`
+   * or `null`, so none of them is exposed on the process.
+   *
+   * An `undefined` option means the slot's default. That qualifies for stdin (`"ignore"`) and stderr (`"inherit"`),
+   * but not for stdout, whose default is `"pipe"`.
+   */
   type NullSubprocess = Subprocess<
     "ignore" | "inherit" | null | undefined,
-    "ignore" | "inherit" | null | undefined,
+    "ignore" | "inherit" | null,
     "ignore" | "inherit" | null | undefined
   >;
   /** Utility type for any process from {@link Bun.spawnSync()} with both stdout and stderr set to `"pipe"` */
   type ReadableSyncSubprocess = SyncSubprocess<"pipe", "pipe">;
-  /** Utility type for any process from {@link Bun.spawnSync()} with both stdout and stderr set to `null` or similar */
-  type NullSyncSubprocess = SyncSubprocess<
-    "ignore" | "inherit" | null | undefined,
-    "ignore" | "inherit" | null | undefined
-  >;
+  /**
+   * Utility type for any process from {@link Bun.spawnSync()} with both stdout and stderr set to `"ignore"`, `"inherit"`
+   * or `null`, so neither is captured.
+   *
+   * An `undefined` option does not qualify: {@link Bun.spawnSync()} defaults both slots to `"pipe"`.
+   */
+  type NullSyncSubprocess = SyncSubprocess<"ignore" | "inherit" | null, "ignore" | "inherit" | null>;
 
   /**
    * Options for creating a pseudo-terminal (PTY).
diff --git a/test/integration/bun-types/bun-types.test.ts b/test/integration/bun-types/bun-types.test.ts
index 05fa801f45e5..e1fca224640e 100644
--- a/test/integration/bun-types/bun-types.test.ts
+++ b/test/integration/bun-types/bun-types.test.ts
@@ -400,6 +400,35 @@ describe("@types/bun integration test", () => {
     });
   });
 
+  // Also runs on debug builds, where the in-process typeTest cases (which cover the whole
+  // fixture directory) are skipped: checks fixture/spawn.ts alone against the packed bun-types.
+  describe("Bun.spawn", () => {
+    test("fixture/spawn.ts type-checks", async () => {
+      const checkDir = join(TEMP_DIR, "spawn-fixture-check");
+      const tsconfig = structuredClone(sourceTsconfig);
+      tsconfig.files = [join(BASE_FIXTURE_DIR, "spawn.ts")];
+      tsconfig.compilerOptions.typeRoots = [join(BASE_FIXTURE_DIR, "node_modules", "@types")];
+      await mkdir(checkDir, { recursive: true });
+      await makeTree(checkDir, {
+        "tsconfig.json": JSON.stringify(tsconfig, null, 2),
+      });
+
+      await using proc = Bun.spawn({
+        cmd: [bunExe(), join(BASE_FIXTURE_DIR, "node_modules", "typescript", "bin", "tsc"), "-p", "."],
+        env: bunEnv,
+        cwd: checkDir,
+        stdout: "pipe",
+        stderr: "pipe",
+      });
+
+      const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+      expect(stderr.trim()).toBe("");
+      expect(stdout.trim()).toBe("");
+      expect(exitCode).toBe(0);
+    });
+  });
+
   describe("Test Globals", () => {
     const code = `
       const test_shouldBeAFunction: Function = test;
diff --git a/test/integration/bun-types/fixture/spawn.ts b/test/integration/bun-types/fixture/spawn.ts
index 2036413158a0..120888a9a87c 100644
--- a/test/integration/bun-types/fixture/spawn.ts
+++ b/test/integration/bun-types/fixture/spawn.ts
@@ -185,6 +185,23 @@ tsd.expectAssignable<WritableSubprocess>(Bun.spawn([], { stdio: ["pipe", "pipe",
 tsd.expectAssignable<WritableSubprocess>(Bun.spawn([], { stdio: ["pipe", "ignore", "inherit"] }));
 tsd.expectAssignable<NullSubprocess>(Bun.spawn([], { stdio: ["ignore", "inherit", "ignore"] }));
 tsd.expectAssignable<NullSubprocess>(Bun.spawn([], { stdio: [null, null, null] }));
+// A Null* process exposes none of its stdio slots. An undefined option means the slot's default: "ignore"
+// for Bun.spawn's stdin and "inherit" for its stderr, but "pipe" for Bun.spawn's stdout and for both
+// Bun.spawnSync slots. So the aliases accept undefined in Bun.spawn's stdin and stderr slots only.
+tsd.expectType<NullSubprocess["stdin"]>().is<undefined>();
+tsd.expectType<NullSubprocess["stdout"]>().is<undefined>();
+tsd.expectType<Bun.NullSyncSubprocess["stdout"]>().is<undefined>();
+tsd.expectType<Bun.NullSyncSubprocess["stderr"]>().is<undefined>();
+tsd.expectAssignable<NullSubprocess>(Bun.spawn([], { stdio: [undefined, "ignore", undefined] }));
+tsd.expectAssignable<NullSubprocess>(Bun.spawn([], { stdout: "ignore" }));
+// @ts-expect-error stdout: undefined means "pipe", so this process has a stdout stream
+tsd.expectAssignable<NullSubprocess>(Bun.spawn([], { stdio: ["ignore", undefined, "ignore"] }));
+tsd.expectAssignable<Bun.NullSyncSubprocess>(Bun.spawnSync([], { stdio: ["ignore", "ignore", "inherit"] }));
+tsd.expectAssignable<Bun.NullSyncSubprocess>(Bun.spawnSync([], { stdio: [null, null, null] }));
+// @ts-expect-error stdout: undefined means "pipe", so this process has a stdout Buffer
+tsd.expectAssignable<Bun.NullSyncSubprocess>(Bun.spawnSync([], { stdio: ["ignore", undefined, "ignore"] }));
+// @ts-expect-error stderr: undefined means "pipe" in spawnSync, so this process has a stderr Buffer
+tsd.expectAssignable<Bun.NullSyncSubprocess>(Bun.spawnSync([], { stdio: ["ignore", "ignore", undefined] }));
 
 tsd.expectAssignable<SyncSubprocess<Bun.SpawnOptions.Readable, Bun.SpawnOptions.Readable>>(Bun.spawnSync([], {}));