diff --git a/CHANGELOG.md b/CHANGELOG.md
index 871141654..08c075a94 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,14 +7,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Added
+
+- Add support for `tailwindcss/lib/util/flattenColorPalette` exports ([#15318](https://github.com/tailwindlabs/tailwindcss/pull/15318))
+
+### Fixed
+
+- Fix dependency related warnings when using `@tailwindcss/postcss` on Windows ([#15321](https://github.com/tailwindlabs/tailwindcss/pull/15321))
 
 ## [4.0.0-beta.6] - 2024-12-06
 
 ### Fixed
 
 - Ensure `@import "…" reference` never generates utilities ([#15307](https://github.com/tailwindlabs/tailwindcss/pull/15307))
-- Fix dependency related warnings when using `@tailwindcss/postcss` on Windows
 
 ## [4.0.0-beta.5] - 2024-12-04
 
diff --git a/packages/tailwindcss/package.json b/packages/tailwindcss/package.json
index 0a36e8f55..37f7c2159 100644
--- a/packages/tailwindcss/package.json
+++ b/packages/tailwindcss/package.json
@@ -31,6 +31,10 @@
       "require": "./src/compat/colors.cts",
       "import": "./src/compat/colors.ts"
     },
+    "./lib/util/flattenColorPalette": {
+      "require": "./src/compat/flatten-color-palette.cts",
+      "import": "./src/compat/flatten-color-palette.ts"
+    },
     "./defaultTheme": {
       "require": "./src/compat/default-theme.cts",
       "import": "./src/compat/default-theme.ts"
@@ -91,6 +95,10 @@
         "require": "./dist/colors.js",
         "import": "./dist/colors.mjs"
       },
+      "./lib/util/flattenColorPalette": {
+        "require": "./dist/flatten-color-palette.js",
+        "import": "./dist/flatten-color-palette.mjs"
+      },
       "./package.json": "./package.json",
       "./index.css": "./index.css",
       "./index": "./index.css",
diff --git a/packages/tailwindcss/src/compat/config.test.ts b/packages/tailwindcss/src/compat/config.test.ts
index b99bc405b..3747f8ae4 100644
--- a/packages/tailwindcss/src/compat/config.test.ts
+++ b/packages/tailwindcss/src/compat/config.test.ts
@@ -1,7 +1,7 @@
 import { describe, expect, test, vi } from 'vitest'
 import { compile, type Config } from '..'
 import { default as plugin } from '../plugin'
-import { flattenColorPalette } from './flatten-color-palette'
+import flattenColorPalette from './flatten-color-palette'
 
 const css = String.raw
 
diff --git a/packages/tailwindcss/src/compat/flatten-color-palette.cts b/packages/tailwindcss/src/compat/flatten-color-palette.cts
new file mode 100644
index 000000000..d8b4be144
--- /dev/null
+++ b/packages/tailwindcss/src/compat/flatten-color-palette.cts
@@ -0,0 +1,8 @@
+import flattenColorPalette from './flatten-color-palette.ts'
+
+// This file exists so that `flatten-color-palette.ts` can be written one time
+// but be compatible with both CJS and ESM. Without it we get a `.default`
+// export when using `require` in CJS.
+
+// @ts-ignore
+export = flattenColorPalette
diff --git a/packages/tailwindcss/src/compat/flatten-color-palette.test.ts b/packages/tailwindcss/src/compat/flatten-color-palette.test.ts
index 3891bbece..7ddda5bd4 100644
--- a/packages/tailwindcss/src/compat/flatten-color-palette.test.ts
+++ b/packages/tailwindcss/src/compat/flatten-color-palette.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from 'vitest'
-import { flattenColorPalette } from './flatten-color-palette'
+import flattenColorPalette from './flatten-color-palette'
 
 test('it should handle private __CSS_VALUES__ to resolve to the right value', () => {
   expect(
diff --git a/packages/tailwindcss/src/compat/flatten-color-palette.ts b/packages/tailwindcss/src/compat/flatten-color-palette.ts
index 03191e2da..ca8845688 100644
--- a/packages/tailwindcss/src/compat/flatten-color-palette.ts
+++ b/packages/tailwindcss/src/compat/flatten-color-palette.ts
@@ -4,7 +4,7 @@ type Colors = {
   [key: string | number]: string | Colors
 }
 
-export function flattenColorPalette(colors: Colors) {
+export default function flattenColorPalette(colors: Colors) {
   let result: Record<string, string> = {}
 
   for (let [root, children] of Object.entries(colors ?? {})) {
diff --git a/packages/tailwindcss/tsup.config.ts b/packages/tailwindcss/tsup.config.ts
index 1a8e23887..59c8bdfa2 100644
--- a/packages/tailwindcss/tsup.config.ts
+++ b/packages/tailwindcss/tsup.config.ts
@@ -10,6 +10,7 @@ export default defineConfig([
       plugin: 'src/plugin.ts',
       colors: 'src/compat/colors.ts',
       'default-theme': 'src/compat/default-theme.ts',
+      'flatten-color-palette': 'src/compat/flatten-color-palette.ts',
     },
   },
   {
@@ -21,6 +22,7 @@ export default defineConfig([
       lib: 'src/index.cts',
       colors: 'src/compat/colors.cts',
       'default-theme': 'src/compat/default-theme.cts',
+      'flatten-color-palette': 'src/compat/flatten-color-palette.cts',
     },
   },
 ])