diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9126b72f7963..bbe07291ca89 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - PostCSS: Ensure that errors in stylesheet dependencies are recoverable ([#17754](https://github.com/tailwindlabs/tailwindcss/pull/17754))
 - Upgrade: Correctly print variants starting with `@` ([#17814](https://github.com/tailwindlabs/tailwindcss/pull/17814))
 - Skip `color-mix(…)` when opacity is `100%` ([#17815](https://github.com/tailwindlabs/tailwindcss/pull/17815))
+- Upgrade: Don't format stylesheets when nothing changed ([#17824](https://github.com/tailwindlabs/tailwindcss/pull/17824))
 
 ## [4.1.4] - 2025-04-14
 
diff --git a/integrations/upgrade/index.test.ts b/integrations/upgrade/index.test.ts
index b52031b3275c..264bd7ff4c3c 100644
--- a/integrations/upgrade/index.test.ts
+++ b/integrations/upgrade/index.test.ts
@@ -1266,7 +1266,6 @@ test(
 
       --- ./src/c.1.css ---
       @import './c.2.css' layer(utilities);
-
       .baz-from-c {
         color: green;
       }
diff --git a/packages/@tailwindcss-upgrade/src/index.ts b/packages/@tailwindcss-upgrade/src/index.ts
index 85b5520a05ee..ed802a2e04d4 100644
--- a/packages/@tailwindcss-upgrade/src/index.ts
+++ b/packages/@tailwindcss-upgrade/src/index.ts
@@ -90,6 +90,7 @@ async function run() {
     let stylesheets = loadResults
       .filter((result) => result.status === 'fulfilled')
       .map((result) => result.value)
+    let originals = new Map(stylesheets.map((sheet) => [sheet, sheet.root.toString()]))
 
     // Analyze the stylesheets
     try {
@@ -213,6 +214,7 @@ async function run() {
 
     // Format nodes
     for (let sheet of stylesheets) {
+      if (originals.get(sheet) === sheet.root.toString()) continue
       await postcss([sortBuckets(), formatNodes()]).process(sheet.root!, { from: sheet.file! })
     }