diff --git a/types/node/fs/promises.d.ts b/types/node/fs/promises.d.ts
index a1c65992c671a4..33c24d16f896c5 100644
--- a/types/node/fs/promises.d.ts
+++ b/types/node/fs/promises.d.ts
@@ -153,7 +153,11 @@ declare module "node:fs/promises" {
          * @return Fulfills with `undefined` upon success.
          */
         appendFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -470,7 +474,11 @@ declare module "node:fs/promises" {
          * @since v10.0.0
          */
         writeFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -1208,8 +1216,7 @@ declare module "node:fs/promises" {
             | string
             | NodeJS.ArrayBufferView
             | Iterable<string | NodeJS.ArrayBufferView>
-            | AsyncIterable<string | NodeJS.ArrayBufferView>
-            | Stream,
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?:
             | (ObjectEncodingOptions & {
                 mode?: Mode | undefined;
@@ -1240,7 +1247,11 @@ declare module "node:fs/promises" {
      */
     function appendFile(
         path: PathLike | FileHandle,
-        data: string | Uint8Array,
+        data:
+            | string
+            | NodeJS.ArrayBufferView
+            | Iterable<string | NodeJS.ArrayBufferView>
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?: (ObjectEncodingOptions & FlagAndOpenMode & { flush?: boolean | undefined }) | BufferEncoding | null,
     ): Promise<void>;
     /**
@@ -1432,7 +1443,6 @@ declare module "node:fs/promises" {
      * When copying a directory to another directory, globs are not supported and
      * behavior is similar to `cp dir1/ dir2/`.
      * @since v16.7.0
-     * @experimental
      * @param src source path to copy.
      * @param dest destination path to copy to.
      * @return Fulfills with `undefined` upon success.
diff --git a/types/node/node-tests/fs.ts b/types/node/node-tests/fs.ts
index 10f0764a9a8022..518d131b236d38 100644
--- a/types/node/node-tests/fs.ts
+++ b/types/node/node-tests/fs.ts
@@ -1,6 +1,7 @@
 import * as fs from "node:fs";
 import {
     access,
+    appendFile as appendFileAsync,
     constants,
     copyFile,
     cp as cpAsync,
@@ -10,6 +11,7 @@ import {
     watch as watchAsync,
     writeFile as writeFileAsync,
 } from "node:fs/promises";
+import { Readable } from "node:stream";
 import { URL } from "node:url";
 import * as util from "node:util";
 import assert = require("node:assert");
@@ -669,17 +671,110 @@ async function testPromisify() {
 }
 
 (async () => {
-    await writeFileAsync("test", "test");
-    await writeFileAsync("test", Buffer.from("test"));
-    await writeFileAsync("test", ["test", "test2"]);
-    await writeFileAsync(
-        "test",
-        async function*() {
-            yield "yeet";
-        }(),
-    );
-    await writeFileAsync("test", process.stdin);
-    await writeFileAsync("test", "test", { flush: true });
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await appendFileAsync("test", buffer);
+    await appendFileAsync("test", "x~yz".repeat(100));
+    await appendFileAsync("test", readable);
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await appendFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await appendFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await appendFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", NaN);
+
+    appendFileAsync("test", new Uint8Array(buffer.buffer));
+    appendFileAsync("test", new Uint16Array(buffer.buffer));
+    appendFileAsync("test", new Uint32Array(buffer.buffer));
+});
+
+(async () => {
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await writeFileAsync("test", buffer);
+    await writeFileAsync("test", "x~yz".repeat(100));
+    await writeFileAsync("test", readable);
+    await writeFileAsync("test", readable, { signal: new AbortController().signal });
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await writeFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await writeFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await writeFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", NaN);
+
+    writeFileAsync("test", new Uint8Array(buffer.buffer));
+    writeFileAsync("test", new Uint16Array(buffer.buffer));
+    writeFileAsync("test", new Uint32Array(buffer.buffer));
 });
 
 {
diff --git a/types/node/v22/fs/promises.d.ts b/types/node/v22/fs/promises.d.ts
index 051ddba4043498..7aa1461fdc4fa9 100644
--- a/types/node/v22/fs/promises.d.ts
+++ b/types/node/v22/fs/promises.d.ts
@@ -111,7 +111,11 @@ declare module "fs/promises" {
          * @return Fulfills with `undefined` upon success.
          */
         appendFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -393,7 +397,11 @@ declare module "fs/promises" {
          * @since v10.0.0
          */
         writeFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -1035,8 +1043,7 @@ declare module "fs/promises" {
             | string
             | NodeJS.ArrayBufferView
             | Iterable<string | NodeJS.ArrayBufferView>
-            | AsyncIterable<string | NodeJS.ArrayBufferView>
-            | Stream,
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?:
             | (ObjectEncodingOptions & {
                 mode?: Mode | undefined;
@@ -1067,7 +1074,11 @@ declare module "fs/promises" {
      */
     function appendFile(
         path: PathLike | FileHandle,
-        data: string | Uint8Array,
+        data:
+            | string
+            | NodeJS.ArrayBufferView
+            | Iterable<string | NodeJS.ArrayBufferView>
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?: (ObjectEncodingOptions & FlagAndOpenMode & { flush?: boolean | undefined }) | BufferEncoding | null,
     ): Promise<void>;
     /**
diff --git a/types/node/v22/test/fs.ts b/types/node/v22/test/fs.ts
index ac1b2b18be083a..f7b33cbeab0015 100644
--- a/types/node/v22/test/fs.ts
+++ b/types/node/v22/test/fs.ts
@@ -1,6 +1,7 @@
 import * as fs from "node:fs";
 import {
     access,
+    appendFile as appendFileAsync,
     constants,
     copyFile,
     cp as cpAsync,
@@ -10,6 +11,7 @@ import {
     watch as watchAsync,
     writeFile as writeFileAsync,
 } from "node:fs/promises";
+import { Readable } from "node:stream";
 import { URL } from "node:url";
 import * as util from "node:util";
 import assert = require("node:assert");
@@ -653,17 +655,110 @@ async function testPromisify() {
 }
 
 (async () => {
-    await writeFileAsync("test", "test");
-    await writeFileAsync("test", Buffer.from("test"));
-    await writeFileAsync("test", ["test", "test2"]);
-    await writeFileAsync(
-        "test",
-        async function*() {
-            yield "yeet";
-        }(),
-    );
-    await writeFileAsync("test", process.stdin);
-    await writeFileAsync("test", "test", { flush: true });
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await appendFileAsync("test", buffer);
+    await appendFileAsync("test", "x~yz".repeat(100));
+    await appendFileAsync("test", readable);
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await appendFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await appendFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await appendFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", NaN);
+
+    appendFileAsync("test", new Uint8Array(buffer.buffer));
+    appendFileAsync("test", new Uint16Array(buffer.buffer));
+    appendFileAsync("test", new Uint32Array(buffer.buffer));
+});
+
+(async () => {
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await writeFileAsync("test", buffer);
+    await writeFileAsync("test", "x~yz".repeat(100));
+    await writeFileAsync("test", readable);
+    await writeFileAsync("test", readable, { signal: new AbortController().signal });
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await writeFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await writeFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await writeFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", NaN);
+
+    writeFileAsync("test", new Uint8Array(buffer.buffer));
+    writeFileAsync("test", new Uint16Array(buffer.buffer));
+    writeFileAsync("test", new Uint32Array(buffer.buffer));
 });
 
 {
diff --git a/types/node/v24/fs/promises.d.ts b/types/node/v24/fs/promises.d.ts
index 6612bff37b2425..237b1f2ef51379 100644
--- a/types/node/v24/fs/promises.d.ts
+++ b/types/node/v24/fs/promises.d.ts
@@ -112,7 +112,11 @@ declare module "fs/promises" {
          * @return Fulfills with `undefined` upon success.
          */
         appendFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -394,7 +398,11 @@ declare module "fs/promises" {
          * @since v10.0.0
          */
         writeFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -1070,8 +1078,7 @@ declare module "fs/promises" {
             | string
             | NodeJS.ArrayBufferView
             | Iterable<string | NodeJS.ArrayBufferView>
-            | AsyncIterable<string | NodeJS.ArrayBufferView>
-            | Stream,
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?:
             | (ObjectEncodingOptions & {
                 mode?: Mode | undefined;
@@ -1102,7 +1109,11 @@ declare module "fs/promises" {
      */
     function appendFile(
         path: PathLike | FileHandle,
-        data: string | Uint8Array,
+        data:
+            | string
+            | NodeJS.ArrayBufferView
+            | Iterable<string | NodeJS.ArrayBufferView>
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?: (ObjectEncodingOptions & FlagAndOpenMode & { flush?: boolean | undefined }) | BufferEncoding | null,
     ): Promise<void>;
     /**
diff --git a/types/node/v24/test/fs.ts b/types/node/v24/test/fs.ts
index 653d234aee5b4f..9969856523ac75 100644
--- a/types/node/v24/test/fs.ts
+++ b/types/node/v24/test/fs.ts
@@ -1,6 +1,7 @@
 import * as fs from "node:fs";
 import {
     access,
+    appendFile as appendFileAsync,
     constants,
     copyFile,
     cp as cpAsync,
@@ -10,6 +11,7 @@ import {
     watch as watchAsync,
     writeFile as writeFileAsync,
 } from "node:fs/promises";
+import { Readable } from "node:stream";
 import { URL } from "node:url";
 import * as util from "node:util";
 import assert = require("node:assert");
@@ -674,17 +676,110 @@ async function testPromisify() {
 }
 
 (async () => {
-    await writeFileAsync("test", "test");
-    await writeFileAsync("test", Buffer.from("test"));
-    await writeFileAsync("test", ["test", "test2"]);
-    await writeFileAsync(
-        "test",
-        async function*() {
-            yield "yeet";
-        }(),
-    );
-    await writeFileAsync("test", process.stdin);
-    await writeFileAsync("test", "test", { flush: true });
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await appendFileAsync("test", buffer);
+    await appendFileAsync("test", "x~yz".repeat(100));
+    await appendFileAsync("test", readable);
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await appendFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await appendFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await appendFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", NaN);
+
+    appendFileAsync("test", new Uint8Array(buffer.buffer));
+    appendFileAsync("test", new Uint16Array(buffer.buffer));
+    appendFileAsync("test", new Uint32Array(buffer.buffer));
+});
+
+(async () => {
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await writeFileAsync("test", buffer);
+    await writeFileAsync("test", "x~yz".repeat(100));
+    await writeFileAsync("test", readable);
+    await writeFileAsync("test", readable, { signal: new AbortController().signal });
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await writeFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await writeFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await writeFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", NaN);
+
+    writeFileAsync("test", new Uint8Array(buffer.buffer));
+    writeFileAsync("test", new Uint16Array(buffer.buffer));
+    writeFileAsync("test", new Uint32Array(buffer.buffer));
 });
 
 {
diff --git a/types/node/v25/fs/promises.d.ts b/types/node/v25/fs/promises.d.ts
index c9c24215addd70..be8bae8c9ec486 100644
--- a/types/node/v25/fs/promises.d.ts
+++ b/types/node/v25/fs/promises.d.ts
@@ -153,7 +153,11 @@ declare module "node:fs/promises" {
          * @return Fulfills with `undefined` upon success.
          */
         appendFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -470,7 +474,11 @@ declare module "node:fs/promises" {
          * @since v10.0.0
          */
         writeFile(
-            data: string | Uint8Array,
+            data:
+                | string
+                | NodeJS.ArrayBufferView
+                | Iterable<string | NodeJS.ArrayBufferView>
+                | AsyncIterable<string | NodeJS.ArrayBufferView>,
             options?:
                 | (ObjectEncodingOptions & Abortable)
                 | BufferEncoding
@@ -1208,8 +1216,7 @@ declare module "node:fs/promises" {
             | string
             | NodeJS.ArrayBufferView
             | Iterable<string | NodeJS.ArrayBufferView>
-            | AsyncIterable<string | NodeJS.ArrayBufferView>
-            | Stream,
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?:
             | (ObjectEncodingOptions & {
                 mode?: Mode | undefined;
@@ -1240,7 +1247,11 @@ declare module "node:fs/promises" {
      */
     function appendFile(
         path: PathLike | FileHandle,
-        data: string | Uint8Array,
+        data:
+            | string
+            | NodeJS.ArrayBufferView
+            | Iterable<string | NodeJS.ArrayBufferView>
+            | AsyncIterable<string | NodeJS.ArrayBufferView>,
         options?: (ObjectEncodingOptions & FlagAndOpenMode & { flush?: boolean | undefined }) | BufferEncoding | null,
     ): Promise<void>;
     /**
@@ -1432,7 +1443,6 @@ declare module "node:fs/promises" {
      * When copying a directory to another directory, globs are not supported and
      * behavior is similar to `cp dir1/ dir2/`.
      * @since v16.7.0
-     * @experimental
      * @param src source path to copy.
      * @param dest destination path to copy to.
      * @return Fulfills with `undefined` upon success.
diff --git a/types/node/v25/node-tests/fs.ts b/types/node/v25/node-tests/fs.ts
index 6ba2a6e850ab9e..603b547acfac05 100644
--- a/types/node/v25/node-tests/fs.ts
+++ b/types/node/v25/node-tests/fs.ts
@@ -1,6 +1,7 @@
 import * as fs from "node:fs";
 import {
     access,
+    appendFile as appendFileAsync,
     constants,
     copyFile,
     cp as cpAsync,
@@ -10,6 +11,7 @@ import {
     watch as watchAsync,
     writeFile as writeFileAsync,
 } from "node:fs/promises";
+import { Readable } from "node:stream";
 import { URL } from "node:url";
 import * as util from "node:util";
 import assert = require("node:assert");
@@ -669,17 +671,110 @@ async function testPromisify() {
 }
 
 (async () => {
-    await writeFileAsync("test", "test");
-    await writeFileAsync("test", Buffer.from("test"));
-    await writeFileAsync("test", ["test", "test2"]);
-    await writeFileAsync(
-        "test",
-        async function*() {
-            yield "yeet";
-        }(),
-    );
-    await writeFileAsync("test", process.stdin);
-    await writeFileAsync("test", "test", { flush: true });
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await appendFileAsync("test", buffer);
+    await appendFileAsync("test", "x~yz".repeat(100));
+    await appendFileAsync("test", readable);
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await appendFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await appendFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await appendFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await appendFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    appendFileAsync("test", NaN);
+
+    appendFileAsync("test", new Uint8Array(buffer.buffer));
+    appendFileAsync("test", new Uint16Array(buffer.buffer));
+    appendFileAsync("test", new Uint32Array(buffer.buffer));
+});
+
+(async () => {
+    const buffer = Buffer.from("");
+    const readable = Readable.from(["a", "b", "c"]);
+
+    await writeFileAsync("test", buffer);
+    await writeFileAsync("test", "x~yz".repeat(100));
+    await writeFileAsync("test", readable);
+    await writeFileAsync("test", readable, { signal: new AbortController().signal });
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid iterables
+    await writeFileAsync("test", [42, 42n, {}, Symbol("42"), true, undefined, null, NaN]);
+    await writeFileAsync("test", Readable.from(["ümlaut", " ", "sechzig"]), "latin1");
+    await writeFileAsync("test", {
+        *[Symbol.iterator]() {
+            yield Buffer.from("a");
+            yield Buffer.from("b");
+            yield Buffer.from("c");
+        },
+    });
+    await writeFileAsync("test", {
+        async *[Symbol.asyncIterator]() {
+            yield "a";
+            yield "b";
+            yield "c";
+        },
+    });
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", 42n);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", {});
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", Symbol("42"));
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", true);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", undefined);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", null);
+    // @ts-expect-error - Invalid value
+    writeFileAsync("test", NaN);
+
+    writeFileAsync("test", new Uint8Array(buffer.buffer));
+    writeFileAsync("test", new Uint16Array(buffer.buffer));
+    writeFileAsync("test", new Uint32Array(buffer.buffer));
 });
 
 {