diff --git a/cli/tests/unit_node/fs_test.ts b/cli/tests/unit_node/fs_test.ts
new file mode 100644
index 0000000000..3e9ad44802
--- /dev/null
+++ b/cli/tests/unit_node/fs_test.ts
@@ -0,0 +1,48 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+import {
+  assert,
+  assertThrows,
+} from "../../../test_util/std/testing/asserts.ts";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { mkdtempSync, readFileSync, writeFileSync } from "node:fs";
+
+Deno.test(
+  "[node/fs writeFileSync] write file without option",
+  () => {
+    const data = "Hello";
+    const filename = mkdtempSync(join(tmpdir(), "foo-")) + "/test.txt";
+
+    writeFileSync(filename, data);
+    const dataRead = readFileSync(filename, "utf8");
+
+    assert(dataRead === "Hello");
+  },
+);
+
+Deno.test(
+  "[node/fs writeFileSync] write file with option ASCII",
+  () => {
+    const data = "Hello";
+    const filename = mkdtempSync(join(tmpdir(), "foo-")) + "/test.txt";
+
+    writeFileSync(filename, data, { encoding: "ascii" });
+    const dataRead = readFileSync(filename, "utf8");
+
+    assert(dataRead === "Hello");
+  },
+);
+
+Deno.test(
+  "[node/fs writeFileSync] write file throws error when encoding is not implemented",
+  () => {
+    const data = "Hello";
+    const filename = mkdtempSync(join(tmpdir(), "foo-")) + "/test.txt";
+
+    assertThrows(
+      () => writeFileSync(filename, data, { encoding: "utf16le" }),
+      'The value "utf16le" is invalid for option "encoding"',
+    );
+  },
+);
diff --git a/ext/node/polyfills/_fs/_fs_common.ts b/ext/node/polyfills/_fs/_fs_common.ts
index c704cd9754..19f0d7d176 100644
--- a/ext/node/polyfills/_fs/_fs_common.ts
+++ b/ext/node/polyfills/_fs/_fs_common.ts
@@ -74,7 +74,7 @@ export function checkEncoding(encoding: Encodings | null): Encodings | null {
   if (!encoding) return null;
 
   encoding = encoding.toLowerCase() as Encodings;
-  if (["utf8", "hex", "base64"].includes(encoding)) return encoding;
+  if (["utf8", "hex", "base64", "ascii"].includes(encoding)) return encoding;
 
   if (encoding === "utf-8") {
     return "utf8";
@@ -85,7 +85,7 @@ export function checkEncoding(encoding: Encodings | null): Encodings | null {
     // node -e "require('fs').readFile('../world.txt', 'buffer', console.log)"
   }
 
-  const notImplementedEncodings = ["utf16le", "latin1", "ascii", "ucs2"];
+  const notImplementedEncodings = ["utf16le", "latin1", "ucs2"];
 
   if (notImplementedEncodings.includes(encoding as string)) {
     notImplemented(`"${encoding}" encoding`);