diff --git a/packages/vite/src/node/plugins/css.ts b/packages/vite/src/node/plugins/css.ts
index 5a1430e4c04954..11d8cb49fe45a0 100644
--- a/packages/vite/src/node/plugins/css.ts
+++ b/packages/vite/src/node/plugins/css.ts
@@ -391,7 +391,7 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
           // this is a shared CSS-only chunk that is empty.
           pureCssChunks.add(chunk.fileName)
         }
-        if (opts.format === 'es' || opts.format === 'cjs') {
+        if (opts.format === 'es' || opts.format === 'cjs' || opts.format === 'system') {
           chunkCSS = await processChunkCSS(chunkCSS, {
             inlined: false,
             minify: true
@@ -450,7 +450,7 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
           .join('|')
           .replace(/\./g, '\\.')
         const emptyChunkRE = new RegExp(
-          opts.format === 'es'
+          opts.format === 'es' || opts.format === 'system'
             ? `\\bimport\\s*"[^"]*(?:${emptyChunkFiles})";\n?`
             : `\\brequire\\(\\s*"[^"]*(?:${emptyChunkFiles})"\\);\n?`,
           'g'