diff --git a/packages/next/next-server/server/config.ts b/packages/next/next-server/server/config.ts
index 34ca86e763d7c..f537c5fb21cd7 100644
--- a/packages/next/next-server/server/config.ts
+++ b/packages/next/next-server/server/config.ts
@@ -99,7 +99,12 @@ function assignDefaults(userConfig: { [key: string]: any }) {
     }
   })
 
-  return { ...defaultConfig, ...userConfig }
+  const result = { ...defaultConfig, ...userConfig }
+  if (result.experimental && result.experimental.css) {
+    // The new CSS support requires granular chunks be enabled.
+    result.experimental.granularChunks = true
+  }
+  return result
 }
 
 function normalizeConfig(phase: string, config: any) {
diff --git a/test/integration/css/next.config.js b/test/integration/css/next.config.js
index 38da3cd3360b3..a00d484fdec00 100644
--- a/test/integration/css/next.config.js
+++ b/test/integration/css/next.config.js
@@ -3,7 +3,11 @@ module.exports = {
     // Make sure entries are not getting disposed.
     maxInactiveAge: 1000 * 60 * 60,
   },
-  experimental: { css: true, granularChunks: true },
+  experimental: {
+    css: true,
+    // Intentionally set false to ensure we force to true.
+    granularChunks: false,
+  },
   webpack(cfg) {
     cfg.devtool = 'source-map'
     return cfg