diff --git a/README.md b/README.md
index 09cb444..2feb3c3 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@ const cookieHeader = cookie.stringifyCookie({ a: "foo", b: "bar" });
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to [`encodeURIComponent`](#encode-and-decode).
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving valid cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
 
 ### cookie.parseSetCookie(str, options)
 
@@ -88,7 +88,7 @@ const setCookieHeader = cookie.stringifySetCookie({
 
 #### Options
 
-- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to [`encodeURIComponent`](#encode-and-decode).
+- `encode` Specifies the function to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1). Defaults to preserving valid cookie-octet values and using [`encodeURIComponent`](#encode-and-decode) otherwise.
 
 ## Cookie object
 
@@ -178,7 +178,7 @@ More information about enforcement levels can be found in [the specification](ht
 Cookie accepts `encode` or `decode` options for processing a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
 Since the value of a cookie has a limited character set (and must be a simple string), these functions are used to transform values into strings suitable for a cookies value.
 
-The default `encode` function is the global `encodeURIComponent`.
+The default `encode` function preserves valid RFC 6265 cookie-octet values and uses the global `encodeURIComponent` otherwise.
 
 The default `decode` function is the global `decodeURIComponent`, wrapped in a `try..catch`. If an error
 is thrown it will return the cookie's original value. If you provide your own encode/decode
diff --git a/src/index.ts b/src/index.ts
index a95a2e9..169953b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -68,6 +68,11 @@ const pathValueRegExp = /^[\u0020-\u003A\u003D-\u007E]*$/;
  */
 const maxAgeRegExp = /^-?\d+$/;
 
+/**
+ * RegExp to match RFC 6265 cookie-octet values that need no URL encoding.
+ */
+const cookieOctetRegExp = /^[!#$%&'()*+\-.\/0-9:<=>?@A-Z[\]\^_`a-z{|}~]*$/;
+
 const __toString = Object.prototype.toString;
 
 const NullObject = /* @__PURE__ */ (() => {
@@ -144,8 +149,9 @@ export interface StringifyOptions {
    * Specifies a function that will be used to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
    * Since value of a cookie has a limited character set (and must be a simple string), this function can be used to encode
    * a value into a string suited for a cookie's value, and should mirror `decode` when parsing.
+   * The default function preserves valid RFC 6265 cookie-octet values and uses `encodeURIComponent` otherwise.
    *
-   * @default encodeURIComponent
+   * @default encode
    */
   encode?: (str: string) => string;
 }
@@ -157,7 +163,7 @@ export function stringifyCookie(
   cookie: Cookies,
   options?: StringifyOptions,
 ): string {
-  const enc = options?.encode || encodeURIComponent;
+  const enc = options?.encode || encode;
   const keys = Object.keys(cookie);
   let str = "";
 
@@ -298,7 +304,7 @@ export function stringifySetCookie(
       ? _name
       : { ..._opts, name: _name, value: String(_val) };
   const options = typeof _val === "object" ? _val : _opts;
-  const enc = options?.encode || encodeURIComponent;
+  const enc = options?.encode || encode;
 
   if (!cookieNameRegExp.test(cookie.name)) {
     throw new TypeError(`argument name is invalid: ${cookie.name}`);
@@ -534,6 +540,13 @@ function decode(str: string): string {
   }
 }
 
+/**
+ * URL-encode string value. Optimized to skip native call for RFC 6265 cookie-octet values.
+ */
+function encode(str: string): string {
+  return cookieOctetRegExp.test(str) ? str : encodeURIComponent(str);
+}
+
 /**
  * Determine if value is a Date.
  */
diff --git a/src/stringify-cookie.bench.ts b/src/stringify-cookie.bench.ts
index 9da3464..a882aaf 100644
--- a/src/stringify-cookie.bench.ts
+++ b/src/stringify-cookie.bench.ts
@@ -10,6 +10,14 @@ describe("cookie.stringifyCookie", () => {
     cookie.stringifyCookie({ foo: "bar" });
   });
 
+  bench("rfc cookie-octets", () => {
+    cookie.stringifyCookie({ foo: "a=b+c/d?x%20" });
+  });
+
+  bench("encode", () => {
+    cookie.stringifyCookie({ foo: "bar baz;%" });
+  });
+
   bench("undefined values", () => {
     cookie.stringifyCookie({
       foo: "bar",
@@ -19,6 +27,14 @@ describe("cookie.stringifyCookie", () => {
     });
   });
 
+  bench("mixed encode", () => {
+    cookie.stringifyCookie({
+      foo: "bar",
+      baz: "quux zap",
+      qux: "quux",
+    });
+  });
+
   const cookies10 = genCookies(10);
   bench("10 cookies", () => {
     cookie.stringifyCookie(cookies10);
diff --git a/src/stringify-cookie.spec.ts b/src/stringify-cookie.spec.ts
index 9edcfde..11f89fa 100644
--- a/src/stringify-cookie.spec.ts
+++ b/src/stringify-cookie.spec.ts
@@ -28,12 +28,57 @@ describe("cookie.stringifyCookie", () => {
     expect(stringifyCookie({ a: "", b: "" })).toEqual("a=; b=");
   });
 
-  it("should URL-encode values by default", () => {
+  it("should encode values with non-cookie-octet chars by default", () => {
     expect(stringifyCookie({ foo: "bar baz" })).toEqual("foo=bar%20baz");
-    expect(stringifyCookie({ foo: "a=b" })).toEqual("foo=a%3Db");
     expect(stringifyCookie({ foo: "hello;world" })).toEqual(
       "foo=hello%3Bworld",
     );
+    expect(stringifyCookie({ foo: 'hello"world' })).toEqual(
+      "foo=hello%22world",
+    );
+    expect(stringifyCookie({ foo: "foo,bar" })).toEqual("foo=foo%2Cbar");
+    expect(stringifyCookie({ foo: "foo\\bar" })).toEqual("foo=foo%5Cbar");
+  });
+
+  it("should pass through cookie-octet values by default", () => {
+    const value =
+      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
+    expect(stringifyCookie({ foo: value })).toEqual(`foo=${value}`);
+  });
+
+  it("should match cookie-octet default encoding", () => {
+    const cookieOctets =
+      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+    const mismatches: string[] = [];
+
+    for (let code = 0; code <= 0xffff; code++) {
+      if (code >= 0xd800 && code <= 0xdfff) continue;
+
+      const value = String.fromCharCode(code);
+      const actual = stringifyCookie({ key: value });
+      const encoded = cookieOctets.includes(value)
+        ? value
+        : encodeURIComponent(value);
+      const expected = `key=${encoded}`;
+
+      if (actual !== expected) {
+        mismatches.push(`${code}: ${actual} !== ${expected}`);
+      }
+    }
+
+    for (const value of ["😄", "𝌆", "𠜎"]) {
+      const actual = stringifyCookie({ key: value });
+      const expected = `key=${encodeURIComponent(value)}`;
+
+      if (actual !== expected) {
+        mismatches.push(`${value}: ${actual} !== ${expected}`);
+      }
+    }
+
+    expect(mismatches).toEqual([]);
   });
 
   it("should error on invalid keys", () => {
diff --git a/src/stringify-set-cookie.spec.ts b/src/stringify-set-cookie.spec.ts
index 92a56ea..3b718f2 100644
--- a/src/stringify-set-cookie.spec.ts
+++ b/src/stringify-set-cookie.spec.ts
@@ -10,12 +10,20 @@ describe("cookie.stringifySetCookie", function () {
     expect(cookie.stringifySetCookie("foo", "bar")).toEqual("foo=bar");
   });
 
-  it("should URL-encode value", function () {
+  it("should encode values with non-cookie-octet chars", function () {
     expect(cookie.stringifySetCookie("foo", "bar +baz")).toEqual(
       "foo=bar%20%2Bbaz",
     );
   });
 
+  it("should pass through cookie-octet values", function () {
+    const value =
+      "!#$%&'()*+-./0123456789:<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]" +
+      "^_`abcdefghijklmnopqrstuvwxyz{|}~";
+
+    expect(cookie.stringifySetCookie("foo", value)).toEqual(`foo=${value}`);
+  });
+
   it("should serialize empty value", function () {
     expect(cookie.stringifySetCookie("foo", "")).toEqual("foo=");
   });