diff --git a/packages/tailwindcss-language-server/src/css/extract-source-directives.ts b/packages/tailwindcss-language-server/src/css/extract-source-directives.ts
index 9de33a9b3..a97e35594 100644
--- a/packages/tailwindcss-language-server/src/css/extract-source-directives.ts
+++ b/packages/tailwindcss-language-server/src/css/extract-source-directives.ts
@@ -1,12 +1,21 @@
 import type { Plugin } from 'postcss'
+import type { SourcePattern } from '../project-locator'
 
-export function extractSourceDirectives(sources: string[]): Plugin {
+export function extractSourceDirectives(sources: SourcePattern[]): Plugin {
   return {
     postcssPlugin: 'extract-at-rules',
     AtRule: {
       source: ({ params }) => {
+        let negated = /^not\s+/.test(params)
+
+        if (negated) params = params.slice(4).trimStart()
+
         if (params[0] !== '"' && params[0] !== "'") return
-        sources.push(params.slice(1, -1))
+
+        sources.push({
+          pattern: params.slice(1, -1),
+          negated,
+        })
       },
     },
   }
diff --git a/packages/tailwindcss-language-server/src/project-locator.test.ts b/packages/tailwindcss-language-server/src/project-locator.test.ts
index ae3598e5b..429f0b27b 100644
--- a/packages/tailwindcss-language-server/src/project-locator.test.ts
+++ b/packages/tailwindcss-language-server/src/project-locator.test.ts
@@ -265,6 +265,40 @@ testLocator({
   ],
 })
 
+testLocator({
+  // TODO: Enable once v4.1 is released
+  options: { skip: true },
+  name: 'automatic content detection with negative custom sources',
+  fs: {
+    'package.json': json`
+      {
+        "dependencies": {
+          "tailwindcss": "0.0.0-insiders.3e53e25",
+          "@tailwindcss/oxide": "0.0.0-insiders.3e53e25"
+        }
+      }
+    `,
+    'src/app.css': css`
+      @import 'tailwindcss';
+      @source './**/*.html';
+      @source not './ignored.html';
+    `,
+    'src/index.html': html`<div class="underline"></div>`,
+    'src/ignored.html': html`<div class="flex"></div>`,
+  },
+  expected: [
+    {
+      config: '/src/app.css',
+      content: [
+        '/*',
+        '/package.json',
+        '/src/index.html',
+        '/src/{**/*.html,**/*.{aspx,astro,cjs,cts,eex,erb,gjs,gts,haml,handlebars,hbs,heex,html,jade,js,json,jsx,liquid,md,mdx,mjs,mts,mustache,njk,nunjucks,php,pug,py,razor,rb,rhtml,rs,slim,svelte,tpl,ts,tsx,twig,vue}}',
+      ],
+    },
+  ],
+})
+
 testFixture('v4/missing-files', [
   //
   {
diff --git a/packages/tailwindcss-language-server/src/project-locator.ts b/packages/tailwindcss-language-server/src/project-locator.ts
index c75ae1dee..c04738bf8 100644
--- a/packages/tailwindcss-language-server/src/project-locator.ts
+++ b/packages/tailwindcss-language-server/src/project-locator.ts
@@ -623,7 +623,7 @@ async function* contentSelectorsFromCssConfig(
 async function* detectContentFiles(
   base: string,
   inputFile: string,
-  sources: string[],
+  sources: SourcePattern[],
   resolver: Resolver,
 ): AsyncIterable<string> {
   try {
@@ -636,9 +636,10 @@ async function* detectContentFiles(
       oxidePath,
       oxideVersion: oxidePackageJson.version,
       basePath: base,
-      sources: sources.map((pattern) => ({
+      sources: sources.map((source) => ({
         base: path.dirname(inputFile),
-        pattern,
+        pattern: source.pattern,
+        negated: source.negated,
       })),
     })
 
@@ -672,11 +673,16 @@ type ConfigEntry = {
   content: ContentItem[]
 }
 
+export interface SourcePattern {
+  pattern: string
+  negated: boolean
+}
+
 class FileEntry {
   content: string | null
   deps: FileEntry[] = []
   realpath: string | null
-  sources: string[] = []
+  sources: SourcePattern[] = []
   meta: TailwindStylesheet | null = null
 
   constructor(