diff --git a/packages/config/src/options.js b/packages/config/src/options.js
index 9d407339b2..fb12f84cbe 100644
--- a/packages/config/src/options.js
+++ b/packages/config/src/options.js
@@ -440,10 +440,8 @@ export function getNuxtConfig (_options) {
     delete options.build.crossorigin
   }
 
-  if (options.build.postcss.plugins) {
+  if (options.build.postcss?.plugins) {
     consola.warn('`postcss.plugins` option has been moved to `postcss.postcssOptions.plugins` for aligning `postcss-loader` format.')
-    options.build.postcss.postcssOptions.plugins = options.build.postcss.plugins
-    delete options.build.postcss.plugins
   }
 
   if (options.buildModules && options.buildModules.includes('@nuxt/postcss8')) {
diff --git a/packages/webpack/src/utils/postcss.js b/packages/webpack/src/utils/postcss.js
index a6c77dfd44..68f4fc52da 100644
--- a/packages/webpack/src/utils/postcss.js
+++ b/packages/webpack/src/utils/postcss.js
@@ -195,12 +195,15 @@ export default class PostcssConfig {
     // Apply default plugins
     if (isPureObject(postcssOptions)) {
       const postcssLoaderOptions = this.postcssLoaderOptions
-      if (postcssLoaderOptions.plugins && !postcssOptions.plugins) {
-        postcssOptions.plugins = postcssLoaderOptions.plugins
+      if (postcssLoaderOptions.plugins) {
+        if (!postcssOptions.plugins || isPureObject(postcssOptions.plugins)) {
+          postcssOptions.plugins = { ...postcssLoaderOptions.plugins || {}, ...postcssOptions.plugins || {} }
+        }
         delete postcssLoaderOptions.plugins
       }
-      if (postcssLoaderOptions.order && !postcssOptions.order) {
-        postcssOptions.order = postcssLoaderOptions.order
+      if ('order' in postcssLoaderOptions) {
+        // Prioritise correct config value
+        postcssOptions.order = postcssOptions.order || postcssLoaderOptions.order
         delete postcssLoaderOptions.order
       }
 
diff --git a/test/fixtures/basic/nuxt.config.js b/test/fixtures/basic/nuxt.config.js
index 3555798026..f7bc4d9809 100644
--- a/test/fixtures/basic/nuxt.config.js
+++ b/test/fixtures/basic/nuxt.config.js
@@ -95,9 +95,12 @@ export default {
           'custom-selectors': true
         }
       },
+      // deliberately invalid config to test normalization
+      plugins: {
+        cssnano: {}
+      },
       postcssOptions: {
         plugins: {
-          cssnano: {},
           [path.resolve(__dirname, 'plugins', 'tailwind.js')]: {}
         }
       }