diff --git a/packages/@headlessui-tailwindcss/CHANGELOG.md b/packages/@headlessui-tailwindcss/CHANGELOG.md
index eb03729..a682f72 100644
--- a/packages/@headlessui-tailwindcss/CHANGELOG.md
+++ b/packages/@headlessui-tailwindcss/CHANGELOG.md
@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Fixed
+
+- Fix bracket order of `not` variants ([#1621](https://github.com/tailwindlabs/headlessui/pull/1621))
 
 ## [0.1.0] - 2022-05-24
 
diff --git a/packages/@headlessui-tailwindcss/jest.config.cjs b/packages/@headlessui-tailwindcss/jest.config.cjs
new file mode 100644
index 0000000..f841b1d
--- /dev/null
+++ b/packages/@headlessui-tailwindcss/jest.config.cjs
@@ -0,0 +1,5 @@
+let create = require('../../jest/create-jest-config.cjs')
+module.exports = create(__dirname, {
+  displayName: ' CSS ',
+  setupFilesAfterEnv: ['./jest.setup.js'],
+})
diff --git a/packages/@headlessui-tailwindcss/jest.setup.js b/packages/@headlessui-tailwindcss/jest.setup.js
new file mode 100644
index 0000000..04649d6
--- /dev/null
+++ b/packages/@headlessui-tailwindcss/jest.setup.js
@@ -0,0 +1,54 @@
+let prettier = require('prettier')
+
+function format(input) {
+  return prettier.format(input.replace(/\n/g, ''), {
+    parser: 'css',
+    printWidth: 100,
+  })
+}
+
+expect.extend({
+  // Compare two CSS strings with all whitespace removed
+  // This is probably naive but it's fast and works well enough.
+  toMatchFormattedCss(received = '', argument = '') {
+    let options = {
+      comment: 'stripped(received) === stripped(argument)',
+      isNot: this.isNot,
+      promise: this.promise,
+    }
+
+    let formattedReceived = format(received)
+    let formattedArgument = format(argument)
+
+    let pass = formattedReceived === formattedArgument
+
+    let message = pass
+      ? () => {
+          return (
+            this.utils.matcherHint('toMatchFormattedCss', undefined, undefined, options) +
+            '\n\n' +
+            `Expected: not ${this.utils.printExpected(formattedReceived)}\n` +
+            `Received: ${this.utils.printReceived(formattedArgument)}`
+          )
+        }
+      : () => {
+          let actual = formattedReceived
+          let expected = formattedArgument
+
+          let diffString = this.utils.diff(expected, actual, {
+            expand: this.expand,
+          })
+
+          return (
+            this.utils.matcherHint('toMatchFormattedCss', undefined, undefined, options) +
+            '\n\n' +
+            (diffString && diffString.includes('- Expect')
+              ? `Difference:\n\n${diffString}`
+              : `Expected: ${this.utils.printExpected(expected)}\n` +
+                `Received: ${this.utils.printReceived(actual)}`)
+          )
+        }
+
+    return { actual: received, message, pass }
+  },
+})
diff --git a/packages/@headlessui-tailwindcss/src/index.test.ts b/packages/@headlessui-tailwindcss/src/index.test.ts
new file mode 100644
index 0000000..e896ae3
--- /dev/null
+++ b/packages/@headlessui-tailwindcss/src/index.test.ts
@@ -0,0 +1,93 @@
+import path from 'path'
+import postcss from 'postcss'
+import tailwind from 'tailwindcss'
+import hui from './index'
+
+let html = String.raw
+let css = String.raw
+
+function run(input: string, config: any, plugin = tailwind) {
+  let { currentTestName } = expect.getState()
+
+  return postcss(plugin(config)).process(input, {
+    from: `${path.resolve(__filename)}?test=${currentTestName}`,
+  })
+}
+
+it('should generate css for an exposed state', async () => {
+  let config = {
+    content: [{ raw: html`<div class="ui-open:underline"></div>` }],
+    plugins: [hui],
+  }
+
+  return run('@tailwind utilities', config).then((result) => {
+    expect(result.css).toMatchFormattedCss(css`
+      .ui-open\:underline[data-headlessui-state~='open'] {
+        text-decoration-line: underline;
+      }
+      :where([data-headlessui-state~='open']) .ui-open\:underline {
+        text-decoration-line: underline;
+      }
+    `)
+  })
+})
+
+it('should generate the inverse "not" css for an exposed state', async () => {
+  let config = {
+    content: [{ raw: html`<div class="ui-not-open:underline"></div>` }],
+    plugins: [hui],
+  }
+
+  return run('@tailwind utilities', config).then((result) => {
+    expect(result.css).toMatchFormattedCss(css`
+      .ui-not-open\:underline[data-headlessui-state]:not([data-headlessui-state~='open']) {
+        text-decoration-line: underline;
+      }
+
+      :where([data-headlessui-state]:not([data-headlessui-state~='open']))
+        .ui-not-open\:underline:not([data-headlessui-state]) {
+        text-decoration-line: underline;
+      }
+    `)
+  })
+})
+
+describe('custom prefix', () => {
+  it('should generate css for an exposed state', async () => {
+    let config = {
+      content: [{ raw: html`<div class="hui-open:underline"></div>` }],
+      plugins: [hui({ prefix: 'hui' })],
+    }
+
+    return run('@tailwind utilities', config).then((result) => {
+      expect(result.css).toMatchFormattedCss(css`
+        .hui-open\:underline[data-headlessui-state~='open'] {
+          text-decoration-line: underline;
+        }
+        :where([data-headlessui-state~='open']) .hui-open\:underline {
+          text-decoration-line: underline;
+        }
+      `)
+    })
+  })
+
+  it('should generate the inverse "not" css for an exposed state', async () => {
+    let config = {
+      content: [{ raw: html`<div class="hui-not-open:underline"></div>` }],
+      plugins: [hui({ prefix: 'hui' })],
+    }
+
+    return run('@tailwind utilities', config).then((result) => {
+      expect(result.css).toMatchFormattedCss(css`
+        .hui-not-open\:underline[data-headlessui-state]:not([data-headlessui-state~='open']) {
+          text-decoration-line: underline;
+        }
+
+        :where([data-headlessui-state]:not([data-headlessui-state~='open']))
+          .hui-not-open\:underline:not([data-headlessui-state]) {
+          text-decoration-line: underline;
+        }
+      `)
+    })
+  })
+})
diff --git a/packages/@headlessui-tailwindcss/src/index.ts b/packages/@headlessui-tailwindcss/src/index.ts
index 50400e6..b825eea 100644
--- a/packages/@headlessui-tailwindcss/src/index.ts
+++ b/packages/@headlessui-tailwindcss/src/index.ts
@@ -29,7 +29,7 @@ export default plugin.withOptions<Options>(({ prefix = 'ui' } = {}) => {
 
       addVariant(`${prefix}-not-${state}`, [
         `&[data-headlessui-state]:not([data-headlessui-state~="${state}"])`,
-        `:where([data-headlessui-state]:not([data-headlessui-state~="${state}"]) &:not([data-headlessui-state]))`,
+        `:where([data-headlessui-state]:not([data-headlessui-state~="${state}"])) &:not([data-headlessui-state])`,
       ])
     }
   }