diff --git a/tests/important-boolean.test.js b/tests/important-boolean.test.js
index 20fc4d1ee598..48a7c10f89f8 100644
--- a/tests/important-boolean.test.js
+++ b/tests/important-boolean.test.js
@@ -1,7 +1,8 @@
 import fs from 'fs'
 import path from 'path'
+import * as sharedState from '../src/lib/sharedState'
 
-import { run, css } from './util/run'
+import { run, css, html } from './util/run'
 
 test('important boolean', () => {
   let config = {
@@ -63,3 +64,74 @@ test('important boolean', () => {
     expect(result.css).toMatchFormattedCss(expected)
   })
 })
+
+// This is in a describe block so we can use `afterEach` :)
+describe('duplicate elision', () => {
+  let filePath = path.resolve(__dirname, './important-boolean-duplicates.test.html')
+
+  afterEach(async () => await fs.promises.unlink(filePath))
+
+  test('important rules are not duplicated when rebuilding', async () => {
+    let config = {
+      important: true,
+      content: [filePath],
+    }
+
+    await fs.promises.writeFile(
+      config.content[0],
+      html`
+        <div class="ml-2"></div>
+        <div class="ml-4"></div>
+      `
+    )
+
+    let input = css`
+      @tailwind utilities;
+    `
+
+    let result = await run(input, config)
+    let allContexts = Array.from(sharedState.contextMap.values())
+
+    let context = allContexts[allContexts.length - 1]
+
+    let ruleCacheSize1 = context.ruleCache.size
+
+    expect(result.css).toMatchFormattedCss(css`
+      .ml-2 {
+        margin-left: 0.5rem !important;
+      }
+      .ml-4 {
+        margin-left: 1rem !important;
+      }
+    `)
+
+    await fs.promises.writeFile(
+      config.content[0],
+      html`
+        <div class="ml-2"></div>
+        <div class="ml-6"></div>
+      `
+    )
+
+    result = await run(input, config)
+
+    let ruleCacheSize2 = context.ruleCache.size
+
+    expect(result.css).toMatchFormattedCss(css`
+      .ml-2 {
+        margin-left: 0.5rem !important;
+      }
+      .ml-4 {
+        margin-left: 1rem !important;
+      }
+      .ml-6 {
+        margin-left: 1.5rem !important;
+      }
+    `)
+
+    // The rule cache was effectively doubling in size previously
+    // because the rule cache was never de-duped
+    // This ensures this behavior doesn't return
+    expect(ruleCacheSize2 - ruleCacheSize1).toBeLessThan(10)
+  })
+})